1 Statistics of Freeway Traffic. 2 Overview The Freeway Performance Measurement System (PeMS)...

1

Statistics of Freeway Traffic

2

Overview

• The Freeway Performance Measurement System (PeMS)

• Computer Lab

• Visualization of Traffic Dynamics

• Visualization and Data Quality

• Travel Time Prediction

• Computer Lab

3

Freeway Performance Measurement System (PeMS)

4

Data Source: Loop Detectors

Measure: Flow, Occupancy, (Velocity)

The PeMS system receives flow and occupancy from approximately 22,000 loops across the state every 30 seconds: 2 GB per day. Currently store 4 TB of data

5

•Managers at any time can have a uniform, and comprehensive assessment of freeway performance.

•Traffic engineers can base their operational decisions on knowledge of the current state of the freeway network.

•Planners can determine whether congestion bottlenecks can be alleviated by improving operations or by minor capital improvements.

•Travelers can obtain the current shortest route and travel time estimates.

•Researchers can validate their theories and calibrate simulation models.

Uses

6

Real-Time Maps

7

Flow Profiles in Space

8

Flow in Space and Time

9

Speed

10

Speed in Space and Time

11

District Summary: VMT

12

13

14

Delay Analysis

15

Detector Health

16

17

Visualizing Traffic Dynamics: Speed

18

Bottleneck Identification

19

Identifying Bad Detectors:Occupancies in Four Adjacent Lanes

20

Travel Time Prediction

21

Velocity Field Portrayed by Loops

22

Daily Travel Time Curves

23

Problem summary and notation

Data available up until time t

Forecast travel time T for trip departing at time t+

T*: the time the trip would take if current conditions persisted into the future

24

T versus T*

9 am =0 3 pm =60

There is a linear relationship between T and T*, but the slope and intercept depend on time of day and on

25

historical mean

current status – T*

regression

Comparison of predictors: =0

26

current status – T*

historical mean

regression

Comparison: = 60