Traffic Model

Traffic flow modeling is an integral part of advance traffic management according to ITS. The model is a computer based tool by which the flow of both recurrent and non-recurrent traffic is modeled and simulated. The modeling and simulation are done to determine the points of congestion in the current road network and to propose solutions to improve the traffic flow by providing alternative use of the existing road networks and modification of signal timing and road lane geometry.

The model is created using the existing road network and simulated with real-time traffic data. The road network can be extracted from high resolution aerial photography or satellite imagery such as IKONOS or QuickBird. The traffic data can be counted using both mechanical and electronic traffic count equipment. The modeling task is accomplished by using suitable commercially available software.

The output of a traffic model usually includes the number of cars traveling on any given road at any given time and the identification of roads and intersections which are congested with traffic during special events and peak hours of the day. The model provides some measure of effectiveness of the participating road networks. This includes Vehicle Miles Traveled (VMT) and Vehicle Hours of Delay (VHD).

A traffic model can be used to simulate planned or proposed changes to an existing road network as well as natural changes in traffic volumes which accompany growing populations. This type of analysis can be done early in the planning stages for a project to determine how changes to a single road or set of roads might affect the broader roadway network. The use of modeling and simulation can therefore be used to more efficiently plan a project and evaluate potential alternatives.

Traffic Modeling Software

A variety of software packages are available for traffic modeling and simulation, but usually they are all based on the same three parts. These are: A representation of the road network, road parameters, and a mathematical formula to distribute trips.

The Oxford-University of Mississippi ITS Project is using two commercially available traffic modeling software packages: TSIS 5.0 and Synchro Plus SimTraffic 5.0.

TSIS

The Traffic Software Integrated System (TSIS) is a collection of software tools for use by traffic engineers and researchers. TSIS 5.0 has been prepared by the ATMS (Advance Traffic Management System division of the ITT Industries Inc. for FHWA (Federal Highway Administration). The software is distributed by PC TRANS, Kansas University Transportation Center.

TSIS 5.0 consists of the following four separate modules:

T-Shell: Provides the GUI of the software that holds the other three modules together.

TRAFED: Traffic Network Editor. The traffic road network is created here with required controller and attributes. Road networks can be drawn directly using available editing tools or by loading Bitmap file (*.bmp).

CORSIM: Corridor Simulator. This module simulates the assigned traffic model and produces output in two ways: (1). An animation file that demonstrates the real world traffic flow of the assigned traffic model and (2) A text file with simulation results.

TRAFVU: Traffic Visualization Utility. This module discusses the animation of the assigned traffic model.

SYNCHRO

Synchro plus SimTraffic 5.0 is an integrated traffic modeling, simulation and signal analysis software. Synchro mostly works like TSIS (CORSIM) but it has the capability of easier data entry, editing and management. For example, bitmap background is used for road network extraction into required scale, where various formats can be used as bitmap background (BMP, JPG, DXF etc.). Data can be entered and edited easily using the lane and volume diagram, timing window and split and phasing diagram. SimTraffic has realistic vehicle simulation capability, where the simulation is displayed with aerial photographs or any other bitmap background. Synchro has colorful, informative Time-Space Diagrams. Splits and offsets can be changed directly on the diagram. Synchro features two styles of time-space diagrams. The bandwidth style shows how traffic might be able to travel down an entire arterial without stopping and the vehicle flow style shows individual vehicles that stop, queue up, and then go. Synchro provides complete and understandable reports of Measure of Effectiveness (MOE) in terms of Delays, Stops, LOS (Level of Service), Queue Penalty, Dilemma Vehicles, Fuel Consumption, and Emissions. This software is one of the mostly used traffic analysis software in the transportation management community.

Traffic Count Data

The Oxford-University of Mississippi ITS project has developed a very good database of real-time traffic count data for most of the important intersections of the City of Oxford and University area. The traffic data was counted in two phases:

Phase-1: Regular Traffic and Phase-2: Traffic during Special Event
To acquire the regular traffic data traffics were counted in two modes for selected intersections. In the first mode, traffic was counted for 2.5 hours during 3 peak times of the day (7:00 AM to 9:30 AM, 11:00 AM to 1:30 PM and 4:00 PM to 6:30 PM). In the second mode, traffic was counted continuously for 12 hours a day (7:30 AM to 7:30 PM).

For traffic data representative of special events, two Olemiss football games in 2002 (Olemiss vs. Memphis and Olemiss vs. Florida) were counted. Traffic was counted for selected intersections for 3.5 hours before the game started and 2.5 hours after the game ended.

The following image shows the locations of the intersections where traffic data were counted.

Slide 1: Traffic count locations

Traffic Models of Oxford-University of Mississippi ITS Project

The Oxford-University of Mississippi ITS project created and simulated models of most of the important intersections of the city and university to study the regular day to day traffic flow and traffic flow during the football game. Models were also created to predict future traffic flow in response to new development works like new apartment complex and new roads.

Regular Traffic Flow Model

The intersections of Jackson Ave. & Fraternity Row, Jackson Ave. & Anderson Road, Jackson Ave & Hathorn Road, Hathorn and Coliseum Drive, and University Ave. and Lamar Ave. were modeled to study the nature of traffic flow during different peak hours of the day. The models were created and simulated using TSIS 5.0 software.

Slide 2: Snapshot of the model created for Jackson Ave - Fraternity Row intersection showing traffic flow during lunch time. Model was created using TSIS 5.0

Slide 3: Snapshot of the model created for Jackson Ave - Fraternity Row intersection showing peak traffic flow during lunch time. Model was created using Synchro 5.0

Slide 4: Snapshot of the model created for Coliseum Drive - Hathorn Road Intersection showing traffic flow during early morning time. Model was created using Synchro 5.0

Event Management Models

Jackson Ave. from the intersections of Sorority Row to Highway 6 was modeled and some of its intersections were simulated with the traffic data obtained before the Memphis game started. Traffic data are also available to simulate the models for viewing the traffic flow during the Florida game.

Models for Traffic Flow Prediction

The City of Oxford is expanding and a lot of new apartments are being constructed in several parts of the city. So, several intersections of the city were modeled and simulated with the estimated increased number of new vehicles due to the construction of new apartments. These models show the nature of future traffic flow in those intersections. The modeled intersections are: Jackson Ave & Anderson Road, and Jackson Ave & Hathorn Road.

In some parts of the city the existing roads have been expanded and renovated. Several new roads have also been constructed in some areas. Models have been created for the proposed new roads and simulated with hypothetical traffic volume data to determine the characteristics of future traffic flow.

Slide 5: Snapshot of the model created for Jackson Ave - Anderson Road intersection showing the traffic flow during lunch time. Model was created using TSIS 5.0

Slide 6: Snapshot of the model created for Jackson Ave - Hathorn Road intersection showing the traffic flow during lunch time with the impact of (1) increment (due to construction of new apartments) of traffic volume due to construction of apartments and (2) presence of new road. Model was created using TSIS 5.0