Traffic Impact Study

“Study to evaluate the impact on a roadway network due to a proposed development”

Proposed Multi-use Development• 100,000 sq.ft Retail Center• 20,000 sq..ft Office Space• 50 Apartment units

Basic Steps Involved:

• Analysis of existing conditions

• Trip Generation and Distribution

• Analysis of future conditions

Analysis of Existing Conditions

“Analysis to assess whether the intersections and roadways within the study area are currently operating at acceptable levels of service”

Steps Involved:

– Traffic Data Collection

– LOS Analysis for Intersections

– Roadway Capacity Analysis

– Queuing Analysis

– Accident Analysis

Trip Generation

“Estimation of trips generated by the proposed

development using the latest edition of Trip

Generation published by ITE or actual traffic

generation counts from a similar existing facility

having the same size and surrounding area

characteristics or from other recognized sources that

provide trip generation data not included in the ITE

manual”

Trip Generation

Types of Trips– Total Trips– Shared (Captured) Trips– Pass-by Trips– Diverted (Linked) Trips– New (Destination) Trips

Total TripsTotal number of trips generated by a land use category

= ITE Trip Rate X Area or Employees or Dwelling Units etc.Example:

Shopping Center: Land Use 820

100,000 sq. ft. Use Average Rate for Adjacent Street Peak

T = 3.75 (X)

T =3.75 (100) = 375 trips 180 enter / 195 exit (48%/52%)

Office: Land Use 710

20,000 sq. ft. Use Average Rate for Adjacent Street Peak

T = 1.49 (X)

T =1.49 (20) = 30 trips 5 enter / 25 exit (17%/83%)

Apartment: Land Use 220

50 units Use Average Rate for Adjacent Street Peak

T = 0.62 (50)

T =0.62 (50) = 31 trips 20 enter / 11 exit (65%/35%)

Shared (Internal)Trips“These are trips which occur on the site where a vehicle will stop at

more than one place on the site. For example, someone destined

for the office on the site may stop at the Shopping Center while

hey are on the site”

Shared Trips = Shared Trips Rate X Total Trips

Example:

Shopping Center 5% x Total Generated = 0.05 x 375 = 18 10 enter / 8 exit

Office 20% x Total Generated = 0.20 x 30 = 6 2 enter / 4 exit

Apartment 39% x Total Generated = 0.39 x 31 = 12 6 enter / 6 exit

INTERNAL TRIPS = 36 18 enter /18 exit

Pass-By TripsThese trips represent vehicles which currently use adjacent

roadways

providing primary access to the new land use / project. These trips,

however, have an ultimate destination other than the project in

question. In this example, the trip started from work with a

destination of home, however on the way, the driver stopped at the

shopping center directly adjacent to their path

Pass-by Trips = ITE Average Pass-by Rate X (Total Generated – Shared)

Sopping Center: 39.5% (375-18) = 141 71 enter / 70 exit

Apartment: 0% (31-12) = 0 0 enter / 0 exit

Office: 0% (30-6) = 0 0 enter / 0 exit

TOTAL PASS-BY = 141 71 enter / 70 enter

Diverted TripsThese trips occur when a vehicle takes a different route

than normal to access a specific facility. Diverted trips are

similar to pass-by trips, but diverted trips occur from

roadways which do not provide direct access to the site.

Instead, one or more streets must be utilized to get to and

from the site

Diverted Trips = Rate x (Total Generated – Shared)

Sopping Center: 32% (375-18) = 114 57 enter / 57 exit

Apartment: 0% (31-12) = 0 0 enter / 0 exit

Office: 0% (30-6) = 0 0 enter / 0 exit

TOTAL PASS-BY = 114 57 enter / 57 enter

New TripsThese trips occur only to access a specific land use such as

the discount superstore. These types of trips will travel to

and from the new site and a single other destination such

as home

New Trips= External Trips-Internal Trips-Pass-by Trips- Diverted trips

Shopping center: 375 – 18 – 141 –114 = 102 42 enter / 60 exit

Office: 30 –6 –0 –0 = 24 3 enter / 21 exit

Apartment: 31 –12 – 0 – 0 = 19 14 enter / 5 exit

TOTAL NEW TRIPS = 145 59 enter / 86 exit

Estimation of Trips using the ITE Trip Generation Manual

Trip Distribution“Distribution of site traffic shall be assigned to the

proposed site driveways and street intersections included

within the study area based on an analysis of the market

area, the area surrounding the site from which the project is

likely to draw a high percentage of its trips established

based upon a travel distance derived from travel time and

travel speed, for the proposed development”

Existing traffic counts, a regional transportation model or

local knowledge can be used to develop traffic distribution.

Example :Using the local knowledge

Analysis of Future Conditions“Analysis to assess whether the intersections and roadways within the study area will operate within the acceptable levels of service for future conditions. Future conditions involve with and without project conditions”

Without Project Traffic

= Ambient traffic growth rate * Existing Traffic + Background project Traffic

With Project Traffic

= Without project traffic + Project traffic

Future Analysisi) LOS Analysis for Intersections

ii) Road Capacity Analysis

iii) Queuing Analysis

iv) Signal Warrant Analysis

Conclusions and Recommendations

i) LOS Results

ii) Capacity Analysis Results

iii) Signal Warrant Analysis Results

Thank You!

Sajeev