KERAJAAN MALAYSIA. Guidelines for the Selection of Speed Limit NTJ 34/2016 JKR Jabatan Kerja Raya Malaysia. Hak Cipta Terpelihara.

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1 N TJ 3 4 / G u i d e l i n es f o r t h e S e le c t i o n o f S p e ed Limit NTJ 34/2016 JKR Jabatan Kerja Raya Malaysia. Hak Cipta Terpelihara. Tidak dibenarkan mengeluarkan mana-mana bahagian artikel, ilustrasi dan isi kandungan buku ini dalam apa jua bentuk dan dengan apa jua cara sama ada secara elektronik, mekanikal, salinan, rakaman atau cara lain sebelum mendapat keizinan bertulis daripada penerbit. KERAJAAN MALAYSIA Guidelines for the Selection of Speed Limit Guidelines for the Selection of Speed Limit Cawangan Jalan Jabatan Kerja Raya Ketua Pengarah Kerja Raya Jabatan Kerja Raya Malaysia Jalan Sultan Salahuddin Kuala Lumpur

2 FOREWORD The Nota Teknik Jalan 34/2016 Guidelines for the Selection of Speed Limit is prepared to assist road authorities to evaluate and determine the appropriate speed limit for a particular road section. This document outlined a rigorous and standard method and procedure in the evaluation process which can be applied to all category of roads. The application of this guideline is to improve the decision making process through applications of selected criteria. The preparation of this document was carried out through research and discussions by a Technical Committee that consisted of members with vast experiences in the design and maintenance of roads. References were also made to relevant Jabatan Kerja Raya s (JKR) guidelines and some best practices by other countries. This document has been presented in a Special Workshop during the 9th Malaysian Road Conference Feedbacks and comments received from stakeholders are carefully considered and incorporated into the document whenever appropriate. For continuous improvement, this NTJ will be reviewed and updated from time to time to incorporate changes in policies and current design requirements. Following which it will then be upgraded as part of the Arahan Teknik Jalan (ATJ) series of documents. This guideline is under the control of Bahagian Inovasi & Standard, Pakar Kejuruteraan Jalan & Jambatan, Cawangan Jalan, JKR Malaysia. In this respect, any comments and feedbacks regarding this document are welcome and should be forwarded to the aforementioned office. Published by: Cawangan Jalan Ibu Pejabat JKR Malaysia Tingkat 21, Menara PJD No. 50, Jalan Tun Razak Kuala Lumpur i

3 ACKNOWLEDGEMENT This document on the Guideline for the Selection of Speed Limit, NTJ 34/2016 was prepared by a Committee consisting of the following members: Ir. Abdul Rahman bin Baharuddin Ahmad Fahmi bin Abd. Ghaffar Abdul Halim bin Mat Daud Siti Nurilam bt Abu Mansor Rohana bt Yaakub Mohd. Harizam bin Ibau Nui Ir. Kaniah bt Ambak Ir. Mohammad Ashaari bin Muda Nurashikin bt Zainal Abidin Sharifah Allyana bt Syed Mohamed Rahim Mohamad Zhaidi bin Baharin Ir. Rohaida bt Rashid (Secretariat) Zety Afrizan bt Mohamad Zaman (Secretariat) Suyati bt Minan (Secretariat) JKR JKR JKR JKR JKR JKR JKR JKR JKR MIROS JKR JKR JKR JKR A special thanks to Ir. Hj. Ab. Manan Embong and Ir. Abdul Mutalif Ab Hameed (former Directors) and Dato Ir. Hj. Che Noor Azeman Yusoff (current Director) of PKJJ, Caw. Jalan, Public Works Department Malaysia for their undivided support and also the utmost appreciation to the above committee members for their relentless effort towards the successful completion and, ultimately, in the culmination of this Manual. The Committee also expresses their gratitude and acknowledges the contributions by all the individuals who took part in the Special Workshop on the Guideline for the Selection of Speed Limit during the preparation of the Document. They are as follows: Ir. Mohamad Shukor bin Che Malek Burhanuddin bin Yusoh Azih Ong Tai Chu Amirul Ain bin Amran JKR LLM MKJR DBKL ii

4 CONTENTS FOREWORD... i ACKNOWLEDGEMENT... ii CONTENTS... iii LIST OF FIGURE... v LIST OF TABLE... v 1. INTRODUCTION General Regulating Driving Speed Objective of Speed Limits Scope and Purpose of this Guideline Terms and Definitions SPEED, SAFETY AND SPEED LIMITS Speed Safe Travel Speed Speed Limit Authorised Agencies Functions of Speed Limit Types of Speed Limit Statutory Speed Limit Local/Zonal Speed Limit Advisory Speed Limit CONCEPT OF APPLICATION General Setting a Speed Limit Flow Chart APPLICATION METHODOLOGY Geometric Road Curvature, R Estimating Free Flow Speed (FFS) for Highways Estimating Free Flow Speed (FFS) for Toll Expressway Traffic and Road Environment Pedestrian Traffic, P Average Weighted Points of Accident Occurrence, A Legal on-street Parking APPLICATION OF GUIDELINE Step Procedure Application Rules OTHER DESIGN CONSIDERATIONS Speed Zone Length Signposting of Speed Zones Advisory Speed iii

5 6.4. School Zones Work Zones Engineering Judgement REFERENCES...36 APPENDIX A: Data Form for 2-Lane Highway APPENDIX B: Data Form for Multilane Highway APPENDIX C: Data Form for Toll Expressway APPENDIX D: A Case Study APPENDIX E: Data Form for Multilane Highway iv

6 LIST OF FIGURE Figure 2.1: Speed and Crash Risk on 60 km/h Roads... 7 Figure 2.2: Speed and Crash Risk on Rural Highways... 7 Figure 2.3: Risk of Fatality on Pedestrian and Vehicle Occupants... 8 Figure 2.4: A Statutory Speed Limit Figure 2.5: A Local Speed Limit Sign Figure 2.6: An Advisory Speed Sign Figure 3.1: Flow Chart on Process for Setting Speed Limit Figure 6.1: Warning Sign with Advisory Speed LIST OF TABLE Table 4.1: Selection of Speed based on Road Curvature, R Table 4.2: Free-flow speed reduction for lane width and paved shoulder width, f LS Table 4.3a: Free-flow speed reduction for access point density, f APDS Table 4.3b: Free-flow speed reduction for access point density, f APDM Table 4.4: Reduction in free-flow speed based on the proportion of motorcycles f M Table 4.5: Free-flow speed reduction for lane width, f LWM Table 4.6: Free-flow speed reduction for median clearance (for inner lane) f MC Table 4.7: Free-flow speed reduction for lane width f LWE Table 4.8: Free-flow speed reduction for median clearance (for inner lane) f LC Table 4.9: Free-flow speed reduction for interchange density, f ID Table 4.10: Speed Selection Table based on Pedestrian Traffic Volume, P Table 4.11a: Speed Selection Table based on Weighted Accident Points for 2-Lane and Multilane Highway Table 4.11b: Speed Selection Table based on Weighted Accident Points for Toll Highway Table 4.12: Speed Selection Table based on Availability of Parking Provision v

7 1.0 INTRODUCTION 1.1 General Motorised vehicle was first invented before the turn of the last century. Traversing on poorly paved road, the maximum speed of travel was quite slow then. Since then, advances in science and technology have brought about faster vehicles and better roads, both of which have served to increase travel speeds for automotive travel. Today, attainable speeds are far more eminent than the maximum speeds that society once generally accepts as reasonable for motorized travel on public roads, yet the speedometers on most motor vehicles display maximum speeds that far surpass the maximum legal speed limits on most roads. Speeding, commonly defined as exceeding the posted speed limit or driving too fast under prevailing conditions, is a primary crash causation factor around the world. In many countries, it often contributes to as many as one-third of fatal crashes. Based on investigations of road traffic accidents in this country, speeding is one of the main road safety problems on our road and contributes as an aggravating factor in most crashes. Human behavior still remains the most influential element in the selection of the preferred speed of travel, overriding all other factors. When a vehicle travels along a particular road, the speed of travel controls the journey time from one destination to another. Over time, the road and its vicinity undergo drastic changes due to the social economic development and diversification of the surrounding land use. With these changes, the speed of travel that has long been enjoyed by drivers may need to be adjusted to suit the new surroundings. Drivers may no longer have the freedom of travelling at their own desired speed. Other factors shall take precedent for the sake of safety. Choosing an appropriate speed limit for a facility can be a polarizing issue for a community. Residents and vulnerable road users generally seek lower speeds to raise quality of life for the community and increased protection for pedestrians and cyclists; motorists seek higher speeds that minimize travel time. Despite the controversy surrounding maximum speed limits, it is clear that the overall goal of setting the speed limit is almost always to increase safety within the context of retaining reasonable mobility. 1.2 Regulating Driving Speed Individual driver decision on the appropriate travel speed may be guided by more than just safety concerns. Travel speed, fuel use and vehicle operating cost are other factors that are also being considered. Nevertheless, whatever the decision made, it will also be evaluated for its contribution to the air pollution. 1

8 High speed driving certainly increases the risk of death and injury for other road users. Speed limits can be used to regulate the driver s speed choices and help drivers in selecting the proper travelling speed along a particular road. In that respect, there are three main reasons why regulatory intervention is warranted: Drivers may not take into account of the risks afflicted on others by their choice of driving speed and habits. Any accident that occurs will incur health problems/bodily injuries and/or vehicle/property damage that is not fully reimbursed by the driver. Drivers may systematically make the wrong choices of speed because of inadequate information or their inability to digest correctly the information presented. Drivers may have a good sense of driving speed and travel time but could underestimate the effect of speed on crash probability and severity. 1.3 Objective of Speed Limits The main objective of setting speed limit is to balance the interests of mobility and safety by ensuring speed limits are safe, appropriate and credible for the category of road and the level of roadside development for which they are set. They must also be nationally consistent. Several purposes behind this objective are as listed below: Balancing travel time and risk of accident Driving speed limit need to be regulated to provide an appropriate balance between the travel time and the risk of accident for a road or a specific section of it. This should allow a reasonable travel time for drivers and at the same time reduces the probability of accident and, the level of severity if accidents do occur. Advise drivers of the proper speed of travel The primary purpose of the speed limit is to advise drivers of the reasonable and safe maximum operating speed under favorable conditions. It provides a basis for enforcement and ought to be fair in the context of traffic law. Improve the overall safety of the road The avoidance of crash and mitigation of the crash outcome will improve the overall level of safety, although there are also many other factors that affect safety (eg. influence of alcohol, drug, roadway geometric etc.). Create uniform and orderly flow of traffic The regulation establishing a common set of rules on the appropriate speed of travel for all drivers using the particular road and create a uniform speed and orderly flow of traffic. The imposition of the speed limit may also have other reasons relating to the economy or conservation plan of the particular area. A secondary objective but equally important is promoting the concept of Safe 2

9 System Approach. Now being widely adopted by many countries around the world, the Safe System Approach represents a significant shift in thinking about road safety. The Safe System Approach recognises that even with the best efforts of prevention by road users, road crashes will still occur therefore, the road system must be designed to be more accommodating of human error and do not cause human death or serious injury. Managing speed to keep the crash forces to survivable levels is key to road safety and the Safe System Approach. 1.4 Scope and Purpose of this Guideline This publication is a guide on selecting the appropriate speed limit for all roads and should be a valuable reference for road authorities, especially those at the district establishment level. It provides the information and standard procedure necessary for practitioners to conduct appropriate analysis and make accurate decisions concerning the setting of speed limits in their jurisdiction. However, the application of the technique and process needs to be applied with flexibility and good judgement to account for the wide variation of the road, environment and traffic conditions. The use of a standard procedure to determine speed limits provides: Consistent methodologies between regions and practitioners. Guidance for data collection and analysis, and the relative importance of the various criteria used in determining speed limits. Consistent correlation of road environments with speed limits. Preservation of the integrity and credibility of speed limits. Standardised documentation, which assists in satisfying accountability and quality management requirements. 1.5 Terms and Definitions The following are terms used in this document. Other references may use or define these terms somewhat differently than as defined below. 1. Basic Speed Law - no person shall operate a motor vehicle at a speed greater than is reasonable and proper for the prevailing conditions th percentile speed - the speed at or below which 85 percent of the sample of free flowing vehicles is traveling. The 85 th percentile of the distribution of observed speeds has been the most frequently used method to determine the operating speed which in turn is used as a guide to set the speed limit. 3. Design speed - the maximum safe speed that can be maintained over a specific segment of road when conditions are favourable that the design features governs. 3

10 4. Operating speed - the speeds at which vehicles are observed operating during free flow conditions. Free flow speeds are those observed from vehicles whose operations are unimpeded by traffic control devices (e.g., traffic signals) or by other vehicles in the traffic stream. 5. Advisory speed is the speed limit recommended by the road authority, often set in areas with many pedestrian activities and on difficult stretches of roads, such as on tight corners or through roadwork zones. Although it is not strictly enforced, liability for any accident while travelling above the speed can be charged for speeding. 6. Speed limit - the maximum lawful vehicle speed for a specific location. There are two types of speed limits, posted speed and statutory speed, definitions of each are provided. 7. Posted speed - one of two speed limit types (statutory speed is the other type); it is the maximum lawful vehicle speed for a particular location as displayed on a regulatory sign. Posted speeds are displayed on regulatory signs in speed values that are multiples of 10 km/h. 8. Statutory speed - one of two speed limit types (posted speed is another type). Numerical speed limits established by law that apply to various classes or categories of roads in the absence of posted speed limits. 9. Speed zone - a speed limit established on the basis of an engineering study for a particular section of road, for which the statutory speed limit is not appropriate. 10. Tolerance - the numerical difference between the speed limit and the minimum speed at which enforcement action is taken. 11. Expressway - is a divided highway for through traffic with full control of access and always with grade separations at all intersections. In rural areas, they apply to the interstate highways for through traffic and form the basic framework of National road transportation for fast travelling. They serve long trip and provide higher speed of travelling and comfort. To maintain this, they are fully access controlled and are designed to highest standards. In urban areas, they form the basic framework of road transportation system in urbanised area through traffic. They also serve relatively long trips and smooth traffic flow and with full access control and complements the Rural Expressway. 12. Highway - constitute the interstate national network for intermediate traffic volumes and complement the expressway network. They usually link up directly or indirectly the Federal Capital, State capitals, large urban centres and points of entry/exit to the country. They serve long to intermediate trip lengths. Speed of travel is not as important as in an 4

11 Expressway but relatively high to medium speed is necessary. Smooth traffic is provided with partial access control. 13. Primary Road - they constitute the major roads forming the basic network of the road transportation system within a state. They serve intermediate trip lengths and medium travelling speeds. Smooth traffic is provided with partial access control. They usually link the State Capitals and district Capitals or other Major Towns. 14. Secondary Road - they constitute the major roads forming the basic network of the road transportation system within a District or Regional Development Areas. They serve intermediate trip lengths with partial access control. They usually link up the major towns within the District or Regional Development Areas. 15. Minor Road - they apply to all roads other than those described above in the rural areas. They form the basic road network within a Land Scheme or other sparsely populated rural area. They also include roads with special functions such as holiday resort roads, security roads or access roads to microwave stations. They serve mainly local traffic with short trip lengths with no access control. 16. Arterial Road - an arterial is a continuous road within partial access control for through traffic within urban areas. Basically it conveys traffic from residential areas to the vicinity of the central business district or from one part of a city to another which does not intend to penetrate the city centre. Arterials do not penetrate identifiable neighbourhoods. Smooth traffic flow is essential since it carries large traffic volumes. 17. Collector Road - a collector road is a road with partial access control designed to serve as a collector or distributor of traffic between the arterial and the local road systems. Collectors are the major roads which penetrate and serve identifiable neighbourhoods, commercial area and industrial areas. 18. Local Road/Local Street - the local street system is the basic road network within a neighbourhood and serves primarily to offer direct access to abutting land. They are links to the collector road and thus serve short trip lengths. Through traffic should be discouraged. 5

12 2.0 SPEED, SAFETY AND SPEED LIMITS 2.1 Speed Vehicle travel speeds determine the time taken to travel from one destination to another. One of the things that a driver desires for is to reach his destination in the shortest duration possible. On the positive side, high speed travel allows efficient movement of people and vehicles through the road network. However, it also affects both the risk of crash involvement and the severity of crashes, and its subsequent injuries thereof. Although speed is not always the main cause of an accident, it is still a critical factor in every serious crash. Speeding was identified as a contributing factor in an estimated 23% of fatal crashes (PDRM, 2013). It is also being accepted that reduction in travel speed would save lives and reduce injuries. Reductions in the average travel speed across the network is the most effective and a swift way to reduce road accident trauma that would produce significant and immediate road safety benefits. Clearly, there is a conflicting demand on speed between the travel time need and the concern for safety. Speed needs to be adjusted to provide some rational balance of these two critical factors, but, at the same time, the adjusted speed must be acceptable by a majority of the drivers to encourage compliance. 2.2 Safe Travel Speed When a driver travels at higher speed that is inappropriate for the prevailing conditions, collision with another vehicle, hitting pedestrians or run off the road is more likely to occur. At high speed, there is less time for driver to react to emergencies and therefore requires a greater distance to stop safely. The risk of a casualty crash approximately doubles with each 5 km/h increase in speed on a 60 km/h speed limited road, or with each 10 km/h increase in speed on 110 km/h rural highways (see Figure 2.1 and 2.2). As such, it is the speed variance and not average travel speed that influences the level of crash involvement. This also means that crash probability increases not only when traveling above the average speed but also below it. A road crash usually results in casualty ranging from minor injury to even death. The severity of injury relates directly to the speed during a crash due to a drastic change in speed (ΔV). Probability of severe injury also increases sharply with the impact speed. During an impact, energy that is released is proportional to the square of the impact speed (kinetic energy equation). This relationship is sufficient to justify the reason for control in speed. Research into the tolerance of the human body to absorb crash energy indicates that speeds would ideally be less than 30 km/h where conflict with people walking 6

13 Relative risk of casualty crash Relative risk of casualty crash and cycling is involved. For cases involving human subjects in vehicles, the tolerable speeds during crashes are less than 50 km/h during vehicle side-impacts and less than 70 km/h during head-on collisions. The conclusions of the research are summarised by Figure Each 5 km/h increase in speed doubles the risk of a casualty crash Figure 2.1: Speed and Crash Risk on 60 km/h Roads (Source: Road Accident Research Unit, University of Adelaide, November 1997) Difference in travelling speed from speed limit (km/h) Each 10 km/h increase in speed doubles the risk of a Figure 2.2: Speed and Crash Risk on Rural Highways (Source: Road Accident Research Unit, University of Adelaide, July 2001) Difference in travelling speed from speed limit (km/h) 7

14 The speed of travel also determines the output quantity of gaseous mission of a vehicle. When travelling faster, more fuel is used and the vehicle emits more of the gases that contribute to air pollution. Some cities around the world impose certain speed limits on their major roads in the effort to control the level of air pollution. Traffic congestion has been the common traffic woes for urban commuters. To improve the situation urban road network need to implement proper traffic management through a systematic and integrated traffic management control. This may include installation of traffic signals and implementation of speed limiters. Apart from the increase in safety, this practice may actually contribute in reducing traffic congestion by improving the traffic flow. Having mentioned all the above, there are other factors that may also justify the need to determine a safe travel speed. Nevertheless, safety still remains the very reason for the management and regulation of speed. Reasonableness, comfort and acceptance by the road users shall be the solemn characteristics of the selected safe speed. Figure 2.3: Risk of Fatality on Pedestrian and Vehicle Occupants (Source: South Australia s Road Safety Strategy 2020, Government of South Australia, May 2011) 2.3 Speed Limit Speed limits are implemented by the road authority to inform motorists of the appropriate driving speeds and these limits are enforced by police or road transport authorities. This is done with an objective to improve road traffic safety and reduce the number of road traffic casualties resulting from traffic collisions. With proper enforcement, speed limit can be an effective traffic safety tool to improve the safety level of an area. Speed limit is a regulatory traffic control means enacted under Section 69 of the Road Transport Act 1987 (Act 333) which is necessary to control speed of vehicles for safety reasons. Malaysia has imposed National Speed Limits for its road networks (90 km/h non-expressways; 110 km/h - Toll expressways). However, 8

15 much lower speed limits are sometimes required at various locations where safety measures are necessary. These sections of road assigned with lower speed limits than the national speed limit are commonly known as speed limit zones. All speed control regulations, including those on speed limits provide the legal basis for adjudication and sanctions for violations of the law. In most cases mandatory speed limits are imposed at specific sections of the road but road authorities may also post advisory speed signs, which do not have the force of law. These signs are specially used to warn motorists of suggested safe speeds for specific conditions at a particular location (e.g., a turn or an intersection approach). Road users are more likely to comply with a speed limit if it is consistent with limits on other roads in the network with similar characteristics, and if limits, in general, reflect the factors that most influence speed choice. The extent of roadside development and the function of a road are the primary determinants of the appropriate speed limit. Consistency is an important aspect in the speed limit selection procedure and should concur with the road users' perceptions of a reasonable speed limit that will influence their willingness to comply. To eliminate any rule-of-thumb or arbitrary approach to the determination of local speed limits, a standard procedure established on the basis of engineering studies is required. Nonetheless, imposition of local speed limits shall only be done if it is deemed necessary for safety reason. 2.4 Authorised Agencies Under Section 69 (1) of the Road Transport Act, the Minister of Transport shall set Statutory Speed Limits for all roads in Malaysia through the Government Official Gazette. However, under Section 69 (2), the Act also empowers the Minister of Works (for all Federal roads) and Local Government authorities (other than Federal roads) to set up local speed limits for roads under their jurisdiction provided that these speed limits (through gazette) do not exceed the statutory speed limit thereof. Changing or imposing local speed limits other than the statutory speed limit shall be based on complaints or requests from: a. Public b. Police c. National Road Safety Council (Majlis Keselamatan Jalan Raya Kebangsaan) d. Local Traffic Advisory Committee (Jawatankuasa Penasihat Lalulintas Tempatan) Speed limits can be quite sensitive issues to certain quarters of the public. Hence, setting or changing of the speed limits must be thoroughly reviewed and shall only be implemented when it is totally justifiable after taking into account all 9

16 relevant factors. The acceptance by the stakeholders must also be pursued to avoid any unnecessary inconveniences. 2.5 Functions of Speed Limit Based on the information above, it can be concluded that the speed limit of a road has two basic functions. These functions are as described below: a. Limiting function - It establishes an upper bound on speed to reduce the probability and severity of crashes. b. Coordinating function - It reduces the dispersion of driving speed, thus reducing the potential vehicular conflicts (this lessens the difference in speed among drivers on the same road but in some cases, may need to control the upper as well as the lower bound speed limit). 2.6 Types of Speed Limit There are several types of speed limits commonly used. The speed limits and their descriptions are given below Statutory Speed Limit Statutory speed limits, also known as the National speed limits (Had Laju Kebangsaan), are based on the concept that uniform categories of highways can operate safely at certain maximum speeds under ideal conditions. The National speed limits are applicable for expressways, federal roads, state roads and municipal roads. The National Speed Limits was enforced on 1 February 1989 following the National Speed Limit Orders 1989 (Perintah Had Laju Kebangsaan 1989). It allows for specific speed limits to be in effect even when it is not practical to post them. 10

17 Figure 2.4: A Statutory Speed Limit Notwithstanding the statutory speed limits above, there are cases where specific speed limits are applicable under certain conditions. The National Motor Vehicle laws specifically require heavy vehicles and buses to abide to certain speed limits. These vehicles must have speed limit stickers describing the allowed speed limits on specific categories of road. For example, a vehicle code might limit speeds to 90 km/h for expressways and 80 km/h on all other roads. Where statutory limits do not fit specific road, traffic, or land use conditions, road authorities have the power to establish local or zonal speed limits to reflect the reasonable and safe maximum operating speeds Local/Zonal Speed Limit These alternative speed limits are usually lower than those prescribed by the statutory limits of the jurisdiction. Legislated through the process of gazette, these speed limits are established on the basis of engineering study, and becoming effective when the limits are posted and properly recorded. The approach and process of setting the zone speed limit is discussed in the following chapters. 11

18 2.6.3 Advisory Speed Limit Figure 2.5: A Local Speed Limit Sign Advisory speeds are used on short sections of road where the physical conditions of the roadway restrict safe operating speed to something lower than the maximum legal speed (e.g., a horizontal curve). Advisory speeds are typically used if: a. the feature that dictates the lower speed is isolated, and b. it is not feasible or desirable to adjust the legal speed for a short section of road. The most common use of advisory speeds is on horizontal curves. In any case, posted regulatory speed limit is not lowered to conform to the proposed advisory speed. However, an advisory speed must not be installed if it is higher than the posted speed limit. In erecting these signs, care should be taken not to install the advisory speed sign too near to a regulatory speed limit sign that it may confuse drivers due to the two different speed value signs being placed too close to each other. Advisory Speed Limit is usually recommended by the road authority, but is not strictly enforced. These speed limits are often set in areas with many pedestrian activities and on difficult stretches of roads, such as on tight corners or through roadwork zones. Having stated that, however, though traveling above the advisory speed limit is not a crime but liability for any accidents which occur on exceeding the advisory speed could still be cited under the basic speed rule (i.e., driving too fast for the prevailing conditions) and can be booked under speeding offences. For the application of advisory speed sign, refer to Chapter 6. 12

19 Figure 2.6: An Advisory Speed Sign 13

20 3.0 CONCEPT OF APPLICATION 3.1 General In establishing a speed limit zone, motorists behaviours are often taken into account. Most drivers are sensible and will naturally drive at a reasonable speed to reach their destination safely. As such, the appropriate guiding principle for evaluating speed limits should be based on the majority concept. The majority speed represents that speed at or below which most of the traffic is moving in ideal road conditions, and is widely accepted as being the suitable speed limit most motorists will comply with. Speed limits that are set to reflect the sensible behaviour of the majority of motorists should encourage compliance and can effectively manage risk. Drivers are more inclined to obeying the posted speed limit and travel at a reasonable free flow speed that generally reduces speed differences among drivers. It also targets limited enforcement resources at the occasional violator who disproportionately contributes to crash risk. There are cases where the free flow speed does not conform to the posted speed limits. Some drivers may behave adversely when speed limits do not reflect road characteristics, resulting in rash decisions and dangerous driving behaviour. And when drivers speeds vary drastically, there are more instances of unsafe passing, rear-end collisions and weaving on multilane roads. That being said, the application of free flow speed alone in the setting of speed limit may not be totally justifiable. Safety of vulnerable road users and hazardous roadside environment are some of the many components that need to be evaluated together as they are very significant in determining the appropriate speed limit of a road section. It s all about finding a balance between all the various factors involved. Within the traffic engineering community worldwide, there are four general approaches to the setting of speed limits. They are briefly described below: a. Engineering approach A two-step processes where a base speed limit is set according to the 85 th percentile speed, the design speed for the road, or other criterion. This base speed limit is adjusted according to traffic and infrastructure conditions (such as pedestrian use, presence of median, etc.). Within the engineering approach itself, there are two methods commonly been adopted: 1. Operating Speed Method; and 2. Road Risk Method. 14

21 Fundamentally, both methods are the same in that a selected base speed limit is adjusted by various factors to determine the recommended speed limit. The main difference between the two methods is that the operating speed method uses the 85 th percentile speed as the base speed limit, and the road risk method uses a base speed limit that is predicated on the functional classification of the road and its setting. b. Expert system approach Speed limits are set by a computer program that uses knowledge and inference procedures that simulate the judgement and behaviour of speed limit experts. Typically, this system is knowledge based, containing accumulated knowledge and experience, and a set of rules for applying the knowledge to each particular situation (the inference procedure). c. Optimization Setting speed limits is to minimize the total societal costs of transport. Travel time, vehicle operating costs, road crashes, traffic noise and air pollution are considered in the determination of optimal speed limits. d. Injury minimization or safe system approach Speed limits are set according to the crash types that are likely to occur, the impact forces that result therefrom, and the human body s tolerance to withstand these forces. As can be comprehended above, setting speed limits can be complex and sometimes controversial. This guide is prepared based on the road risk method under the engineering approach. This method is adopted due to its practicality and easily applicable by most users, especially technical staffs at district and state levels. The engineering approach may require the use of sound engineering judgment based on the engineering and traffic investigation. Compilation of quality data and good documentation should provide support for the judgments that are made. Under the road risk method for setting speed limits, the extent of roadside development and functions of road are the primary determinants of the appropriate speed limit. Although road geometry is also an important factor in determining speed limit, it is secondary to roadside development. 3.2 Setting a Speed Limit The determination of speed limit requires data collection and systematic analysis. The data collection includes measurement of prevailing traffic speeds, crash data, and information on highway, traffic and roadside conditions. The process of setting a speed limit involves a two-part analysis where each part is independent of each other, but both are critically important in the computation. The two-part analysis is: 15

22 a. Determination of safe speed and free flow speed based on geometric configuration; and b. Selecting safe speeds based on the risks associated with the road environment and existing traffic conditions. The first part of the analysis is to determine the preferred speed of travel under the prevailing conditions of the road. The prevailing conditions are the road parameters that affect the travel speed along the road. Free flow speed is affected by many factors which include, among others the road curvature, lane width and no. of accesses. This part is fully described and explained in the following chapter. While the second part covers various aspects of the traffic and road environment, this part alone looks at several criteria that have significant effects on the level of service and safety of the road. A list of pre-set speed limits is proposed and selection is made depending on the frequency or intensity of the criterion under consideration. This part of the analysis is specifically covered in Chapter Flow Chart The process of setting a speed limit for a particular section of a road is presented and summarised by the flow chart in Figure

23 Step 1 Step 2 Step 3 Step 4 Step 5 Step 6 Figure 3.1: Flow Chart on Process for Setting Speed Limit 17

24 4.0 APPLICATION METHODOLOGY As presented in the flow chart in Figure 3.1, the two-part analysis in the setting of speed limit is based on geometric features and, traffic and road environment elements. This chapter shall describe in some detail, the calculations and procedures involved in each part. 4.1 Geometric The most influential feature of a road that affects the traveling speed is the geometric elements. These geometric elements are used to determine the selected or preferred speed by drivers. Methodology used in the Malaysian Highway Capacity Manual is adopted in determining this preferred speed. The following elements are used: Road Curvature, R Road curvature or radius of curve is one of the geometric elements that affect speed. It is an important control value in designing for comfort and safe operation. The higher the value of curvature provided, the higher the travel speed. Road curvature, R, should normally be obtained from design or as-built drawing if available; otherwise it should be obtained from a survey done on site. Table 4.1: Selection of Speed based on Road Curvature Selected Speed Radius, R (m) 90 km/h 80 km/h 70 km/h 60 km/h 50 km/h R > < R < < R < < R < 175 R < Estimating Free Flow Speed (FFS) for Highways Flow rate is defined as the rate at which traffic traverses a freeway segment, in vehicles per hour or passenger cars per hour. Free-flow speed (FFS) is actually defined as the speed that occurs when density and flow are zero. The FFS can be estimated indirectly when field data is not available. 18

25 FFS = BFFS - f LS - f APDS - f M FFS = BFFS - f LWM - f APDM - f MC - f LP (2-Lane Highway) (Multilane Highway) Where; BFFS = Base free-flow speed (km/h) f LS = Speed adjustment for lane width and shoulder width (Table 4.2) f APDS = Speed adjustment for access points density (Table 4.3a) f M = Speed adjustment for proportion of motorcycles (Table 4.4) f LWM = Speed adjustment for lane width (Table 4.5) f APDM = Speed adjustment for access point density (Table 4.3b) f MC = Speed adjustment for median clearance of inner lane (Table 4.6) f LP = Speed adjustment for lane position (f LP always zero since this analysis considers the inner most lane for multilane highway) a. Base Free Flow Speed (BFFS) In order to estimate FFS, the operating conditions of the facility must be characterised in terms of a base free-flow speed (BFFS) that reflects the character of traffic and the alignment of the facility. Estimates of BFFS can be developed based on speed data and local knowledge of operating conditions for similar facilities. In this manual, the BFFS values will be 90 km/h for 2-lane highway and 100 km/h for multilane highway. b. Speed adjustment for Lane Width and Shoulder Width, f LS The adjustment to the estimated FFS relates to the effects of lane and shoulder widths. Base conditions for a 2-lane highway require 3.65 m lane width and 1.8 m shoulder width. Table 4.2 lists the adjustments to the estimated FFS for various lane and shoulder widths. The data in Table 4.2 indicates, for example, that in 2-lane highway with 3.5 m lanes and full shoulder width has an FFS that is 0.7 km/h less than a highway with base lane and shoulder widths. Table 4.2: Free-flow speed reduction for lane width and paved shoulder width, f LS Reduction in free-flow speed (km/h) Lane width (m) Paved Shoulder (m)

26 (Source: Malaysian HCM 2011) c. Speed adjustment for Access point Density, f APDS / f APDM Table 4.3a and Table 4.3b present the adjustment to FFS based on various levels of access point density for 2-lane highway and multilane highway respectively. The access point density for a 2-lane highway is determined by dividing the total number of access points (i.e., intersections and driveways) on both sides of the roadway segment by the length of the segment in kilometres. Whereas the access point density for a multilane highway is determined by dividing the total number of access points on the left side of the roadway in the direction of travel by the segment length. In both cases, an intersection or driveway should only be included if it influences traffic flow. Access points unnoticed by the driver or those with little activity should not be included in determining access point density. Table 4.3a: Free-flow speed reduction for access point density, f APDS Access points/km Reduction in free-flow speed (km/h) (Source: Malaysian HCM 2011) Table 4.3b: Free-flow speed reduction for access point density, f APDM Access points/km Reduction in free-flow speed (km/h) (Source: Malaysian HCM 2011) 20

27 d. Speed adjustment for Proportion of Motorcycles, f M Under Malaysian traffic condition, there is a need to consider motorcycles for the analysis especially when the percentage of motorcycles is high. The presence of motorcycles can significantly affect the mean FFS. Table 4.4 shows the reduction of free-flow based on the proportion of motorcycles. Table 4.4: Reduction in free-flow speed based on the proportion of motorcycles, f M Reduction in free-flow speed (km/h) Proportion of BFFS estimated based on all BFFS estimated based on Motorcycles vehicles except motorcycles passenger cars only (Source: Malaysian HCM 2011) e. Speed adjustment for Lane Width, f LWM The effect of lane width is only applicable for multilane highway and the base condition with regard to lane width is 3.65 m. Lane width less than 3.65 m will reduce FFS, but lane width greater than 3.65 m is assumed to have no effect on FFS. Table 4.5 presents the adjustment of lane width to estimate the FFS for multilane highways. Table 4.5: Free-flow speed reduction for lane width, f LWM Lane width (m) Reduction in free-flow speed (km/h) (Source: Malaysian HCM 2011) f. Speed adjustment for Median Clearance, f MC For multilane highway consideration is only given to the inner most lane. Table 4.6 shows the speed reduction due to median (lateral) clearance for inner lane. Lateral clearance from the right edge of inner lane is the median clearance. 21

28 In this manual, the analysis is only applicable for the inner lane where the speed is higher.the base condition with regard to median clearance for multilane highway is 1.80 m. Median clearance with width less than 1.80 m will reduce free-flow speed, but median clearance greater than 1.80 m is assumed to have no effect on FFS. For undivided multilane highway, the median clearance on the right edge is always zero with a reduction of 7.5 km/h. Table 4.6: Free-flow speed reduction for median clearance (for inner lane), f MC Lateral clearance (m) Reduction in free-flow speed (km/h) (Source: Malaysian HCM 2011) g. Speed Adjustment for Lane Position, f LP The effect of lane position needs to be considered for highway segments with two or three lanes (per direction). The analysis considers the determination of the highest possible speed and, therefore, is applicable to the innermost lane of the multilane highway where f LP equals to zero Estimating Free Flow Speed (FFS) for Toll Expressway Free-flow speed (FFS) is the term used to describe the average speed that a motorist would travel if there were no congestion or other adverse conditions (such as bad weather). At sites, FFS is measured based on space 22

29 mean speed with headway more than 8 s. However, in the absence of measured data, FFS can be estimated directly using equation. Factors affecting FFS are lane width, lateral clearance, interchange density and lane position. FFS = BFFS - f LWE - f LC - f ID - f LPE (Toll Expressway) Where; BFFS = Base free-flow speed (km/h) f LWE = Speed adjustment for lane width (Table 4.7) f LC = Speed adjustment for median clearance for inner lane (Table 4.8) f ID = Speed adjustment for interchange density (Table 4.9) f LPE = Speed adjustment for lane position (f LPE always zero since the inner most lane of the multilane highway is considered) a. Base Free Flow Speed (BFFS) Based on FFS equation, estimation of FFS for an existing or future toll expressway is accomplished by adjusting a BFFS to reflect the influence of four factors which are lane width, lateral clearance, interchange density and lane position. Thus, the analyst is required to select an appropriate BFFS as a starting point. Based on the empirical data, the recommended value for BFFS is 120 km/h. b. Speed Adjustment for Lane Width, f LWE The base condition for lane width is 3.75 m or greater. When the lane width is less than 3.75 m, the BFFS (e.g., 120 km/h) is reduced. Adjustments to reflect the effect of narrower lane widths are given in Table 4.7. Table 4.7: Free-flow speed reduction for lane width Lane width (m) Reduction in free-flow speed (km/h) > (Source: Malaysian HCM 2011) c. Speed Adjustment for Median Clearance, f LC No adjustments are made for median clearance greater than 1.0 m, however when the median clearance is less than 1.0 m, the BFFS is reduced. Adjustments to reflect the effect of narrower median clearance (for inner lane) are given in Table

30 Table 4.8: Free-flow speed reduction for median clearance (for inner lane), f LC Median clearance (m) Reduction in free-flow speed (km/h) (Source: Malaysian HCM 2011) d. Speed Adjustment for Interchange Density, f ID The base condition for interchange density is zero interchanges per kilometre, or 5 km of interchange spacing. BFFS is reduced when interchange density becomes greater. Adjustments to reflect the effect of interchange density are provided in Table 4.9. Table 4.9: Free-flow speed reduction for interchange density, f ID Interchange points/km Reduction in free-flow speed (km/h) (Source: Malaysian HCM 2011) e. Speed Adjustment for Lane Position, f LPE The effect of lane position needs to be considered for highway segments with two or three lanes (per direction). The analysis considers the determination of the highest possible speed and, therefore, is applicable to the inner most lane of the multilane highway where f LPE equals to zero. 4.2 Traffic and Road Environment An important factor in setting a speed limit is what the road looks like to the road users. This is influenced by the environment through which the road passes. Safe travelling speed may be based on the level of accident risk. Generally, most road users will expect lower speed limits where they can see that there are more potential risks. The presence of vulnerable road users and constraints within the road carriageway can significantly affect the desirable speed of drivers. Incidentally, the physical limitations and perception of the degree of hazard provide some form of indirect speed control. However, not all drivers have the same perception of the hazards of speed as do vulnerable road users. An appropriate safe speed based on the traffic and environmental factors can be established through the following criteria: 24