Acceleration Behavior Study and Acceleration Length Design for Metered On-Ramps

Transcription

1 Acceleration Behavior Study and Acceleration Length Design for Metered On-Ramps Guangchuan Yang Graduate Research Assistant Reno, NV89557 October 29,

2 2 Presentation Overview Background Introduction Data Collection and Processing Acceleration Characteristics Acceleration Length Prediction Recommendations

3 3 Metered On-Ramp Freeway Mainline Safety Issues Proper ramp signal location Queue Spillback

4 4 Problem Statement Issues with existing guidelines Out-of-date acceleration data Un-realistic assumptions Based on un-metered ramps Challenges Measurement error Drivers behavior Large sample

5 Research Objectives 5 Investigate the impacts of ramp metering on drivers acceleration behavior Develop method for acceleration length design

6 6 Speed Data in Need

7 Camera Layout 7 (Artesia Blvd to NB 405, Los Angeles)

8 Field Data Collection 8

9 Field Data Collection 9 Stopwatch for time synchronization

10 Piecewise-Constant Acceleration Model 10 t1 t2 t3 a (t1~t2) a (t2~t3) S1 S2 S3 T 1 2 T 1 2 T 2 2 T 2 2 T 3 2 T 3 2 T1 T2 T3 V1 V2 V3 v 0 v S1 v S1+S2 v S1+S2+S3 a (0~S1) a (S1~S2) a (S2~S3)

11 Example of An Individual Sample (Speed vs. Distance Profile) 11

12 Example of An Individual Sample (Acceleration vs. Distance Profile) 12

13 13 Ramp Metering & Acceleration Behavior

14 Meter On vs. Meter Off (Speed Profiles) 14 Artesia Blvd. to NB 405, Caltrans District 7

15 Meter On vs. Meter Off (Acceleration Profiles) 15 Artesia Blvd. to NB 405, Caltrans District 7

16 Short vs. Long Existing Acceleration Length (Speed Profiles) 16 Artesia Blvd. to NB 405 vs. Rosecrans Ave. to NB 710, Caltrans District 7

17 Short vs. Long Existing Acceleration Length (Acceleration Profiles) 17 Artesia Blvd. to NB 405 vs. Rosecrans Ave. to NB 710, Caltrans District 7

18 18 Major Findings from Acceleration Study Acceleration rate is not constant; kinematic equation cannot be directly used for acceleration length calculation. Drivers usually accelerate at a higher acceleration rate when the speed is lower, and vice versa. Ramp metering tends to affect drivers acceleration behavior by producing higher acceleration rates. Existing acceleration length is the primary factor that affect acceleration capability, and consequently the required acceleration lengths.

19 Acceleration Length Prediction Method 19

20 Acceleration Length Prediction Method th Percentile L = 0.021*V R 2 = th Percentile L = *V R 2 = th Percentile L = *V R 2 =

21 Model Validation (Probe Vehicle with GPS Trajectory Recorder) 21

22 Model Validation (GPS Trajectory) 22

23 Model Validation (GPS Data ft.) 23

24 Model Validation (GPS Trajectory vs. Regression Prediction) 24 Error due to speed limit or freeway congestion

25 Mean Percentage Error (MPE) 25

26 Model Validation 26

27 Acceleration Length Predictions 27

28 28 Dual-Level Design Standard Aggressive Design Standard Based on the data from four metered on-ramps with short existing acceleration length For ramps with insufficient ramp space or recurrent ramp queue overspill issue Conservative Design Standard Based on the data from three metered on-ramps with long existing acceleration length For ramps that have sufficient space

29 29 Acceleration Length Design Recommendations Sample Size (number of vehicles) Aggressive: 844 Conservative: 814

30 Acceleration Length Compared to AASHTO 30

31 31 Recommendations to Acceleration Length Design Dual-level design standard to accommodate the unique requirements of metered on-ramps. AASHTO Green Book design guidance could be reduced by 10 percent to 35 percent for passenger cars at metered on-ramps.

32 32 Acknowledgements This research is sponsored by California Department of Transportation (Caltrans). The presenter thanks Dr. Hao Xu, Prof. Zong Tian form UNR CATER, and Dr. Zhongren Wang from Caltrans Head Quarter for their constructive comments. Thanks to Caltrans engineers and the UNR Research Team for their help with field data collection.

33 Questions and Suggestions 33 Guangchuan Yang UNR CATER