Companion Guide to Video October 2013

www.fhwa.dot.gov/federal-aidessentials

As communities grow, so do problems with 

traffic congestion and roadway maintenance. 

These issues can result in unpredictable travel 

times, increased traffic collisions, growing driver 

frustration, and higher levels of air pollution. 

What are your agency's plans to monitor and 

reduce community traffic congestion? 

To best understand the cause of congestion and 

to identify solutions, such as the addition of a 

traffic signal or a new road, engineers conduct 

traffic studies. A traffic study helps engineers 

generate “What if?” scenarios and predict the 

impact of a potential transportation 

improvement on the traveling public. 

Additionally, operations personnel can use the 

study to make travel times more predictable 

each day and throughout the year. 

Techniques for conducting traffic studies can be 

found in the Highway Capacity Manual and 

FHWA's Traffic Analysis Toolbox. But as 

methods of analysis continue to quickly evolve, 

the challenge for most agencies is how to 

effectively use newer, more sophisticated 

analysis and data collection techniques, such as 

travel data collected from cell phones, GPS, and 

Bluetooth devices. 

Let's look at the process for conducting traffic 

studies and the innovative techniques used by 

two agencies to study traffic and make smart 

investment decisions. 

The guidelines for developing a traffic analysis 

begin with a scope for the analysis and end with 

the alternative analysis and final report. 

When preparing a scope for the analysis, 

engineers verify that the study is appropriate 

for the transportation goal and that resources 

are available to complete the study. For 

example, the scope includes identifying 

transportation objectives, selecting the

analytical model, and identifying staff 

resources. The next step involves the collection 

of data about vehicles, bicycles and pedestrians, 

peak and seasonal period traffic, and overall 

Project Development

Operations

Scoping and Conducting a Traffic Study to Meet 

Community Needs

Traffic studies predict project impacts and provide analysis of alternative 

solutions
Federal-aid Essentials for Local Public Agencies

roadway demand. The likelihood that your 

agency's traffic study will reliably predict the 

effect of an improvement depends on the data 

it uses. Rather than relying on overly simplistic 

data collected during the peak hour, start 

investigating new and emerging sources. 

Conduct field checks, reach out to stakeholders 

who are knowledgeable about local conditions, 

and investigate the availability of road-user data 

services. Your State department of 

transportation or metropolitan planning 

organization may already subscribe to such a 

data service. 

Next, base-model development, error checking, 

and calibration help develop a model that will 

accurately predict changes in travel time and 

wait-queues for the “What if?” scenarios. Error 

checking is necessary to eliminate coding errors, 

while calibration allows the analyst to modify 

parameters to closely approximate regional or 

local conditions. 

Now, let's see how two agencies approach the 

questions related to project scope and data 

collection. In our first example, the developer of 

a small shopping center in town proposes the 

addition of a new traffic signal to minimize its 

impact on the surrounding community. 

While the proposed traffic signal is the 

traditional solution, when a signal was installed 

at a similar development the previous year, it 

resulted in long queues and delays. This time, 

agency personnel want to see a traffic study 

before making any decisions. 

During a preliminary review meeting, the 

metropolitan planning organization introduces 

a newly acquired data source for current 

demand and travel times. The team also learns 

that road users encounter congestion from 7:30 

a.m. to 9:30 a.m. 

The team asks the developer to use the new 

data source to assess overall roadway demand 

and queue lengths for the rush hour's entire 

two-hour duration. 

The analysis reveals that the proposed traffic 

signal would create long queues at the entrance 

to the shopping center, as well as a two-fold 

increase in travel time on the street. The 

optimal solution results in the addition of a 

second entrance to manage access and the 

coordination of traffic signals for a two-mile 

stretch of the roadway. 

In our second example, a city is considering the 

addition of a traffic lane and other roadway 

improvements to alleviate congestion along a 

busy corridor. Existing data indicates that daily 

congestion lasts 3 to 4 hours and is exacerbated 

by roadway incidents and bad weather. 

As one of the first steps in the traffic study, the 

city traffic engineer elects to use a simulation 

model. The advantage of the model is that it 

can address long periods of congestion along 

with any contributing factors, such as traffic 

incidents and weather effects. This approach 

requires additional data inputs beyond the city's 

current records. 

While investigating other options, the city 

traffic engineer learns that the metropolitan 

planning organization has access to both a 

regional simulation model and the necessary 

input data from a commercial, third-party 

source. 
Federal-aid Essentials for Local Public Agencies

Using the model and data, the city formulated 

numerous incident management and weather 

responses. Ultimately, they found significant 

reductions in congestion by implementing 

intelligent transportation system technology, 

which was cheaper than adding more traffic 

lanes. 

As the examples illustrate, agencies should 

conduct traffic studies to evaluate the costs and 

benefits of proposed road improvements. As 

our examples illustrate, when agencies use 

more robust field data and select the right 

analysis tool for the project, they develop more 

reliable analyses to help them make better 

decisions. 

The Highway Capacity Manual and FHWA's 

Traffic Analysis Toolbox contain methods for 

conducting traffic studies, and the Federal 

Highway Administration recommends that 

agencies use these when working on any traffic 

analysis.
Federal-aid Essentials for Local Public Agencies

The content of this 

document is not a 

substitute for 

information obtained 

from State departments 

of transportation, 

appropriate FHWA 

Division Offices, and 

applicable laws. 

Scenarios have been 

simplified for emphasis 

and do not necessarily 

reflect the actual range of 

requirements applicable 

to the scenario or this 

topic. This document

was created under 

contract number 

DTFH61-11-D-00025 by 

the Federal Highway 

Administration, U.S. 

Department of 

Transportation, and is 

offered to the public to 

heighten and focus 

awareness of Federal-aid 

requirements within the 

local public agencies 

community and 

reinforces the 

importance of these 

necessary policies, 

procedures, and 

practices.

This Companion Resource 

is the script content for 

the video production of 

the same name. 

Additional Resources

• TRB 2010 Highway Capacity Manual 

http://ops.fhwa.dot.gov/trafficanalysistools/

• FHWA Traffic Analysis Toolbox 

http://hcm.trb.org/