Traffic Impact Analysis

1
Lecture 8

• Traffic Impact Analysis

2
General Steps in EIA Process
Formulate project
Identify potentially significant environmental
impacts
Evaluate impacts
Develop mitigation measures
Report / Revise
Decision
3
Impact Identification vs. Impact Evaluation

• Impact Identification Phase
• Objective identify potentially significant
  impacts for further analysis
• Impact Analysis Phase
• Objectives
• evaluate magnitude and duration of all
  potentially significant impacts in comparison to
  thresholds of significance and
• develop mitigation measures to reduce impacts

4
Motorized Vehicle Traffic

• Problem new development adds motor vehicle
  traffic to highway network
• Potential effects
• Increased social costs
• Congestion longer commuting times
• Safety collisions with vehicles and pedestrians
• Increased environmental costs
• Emissions to atmosphere
• Higher ambient noise levels

5
Typical Daily Traffic Pattern
6
Traffic Impact Analysis

• Assess the effects of a developments traffic on
  the transportation network in the community
• Help evaluate whether the development is
  appropriate for a site and what type of
  transportation improvements may be necessary

7
Uses of Traffic Impact Analysis

• Assist communities in land use decision making. 
• Forecast additional traffic associated with new
  development. 
• Determine necessary improvements to accommodate
  development, including need for public transit.
• Assist in allocating scarce resources to areas
  which need improvements. 
• Help to ensure safe and reasonable traffic
  conditions on streets after the development is
  complete. 
• Protect the substantial community investment in
  the street system.

8
Basic Definitions

• Trip a one direction motorized vehicle movement
• Primary (or unlinked) trip goes directly
  between the primary purposes of home, work, or
  school
• Secondary (or linked) trip one or more stops
  along the way to primary destination
• Pass-by trip deviates from roadway to a site for
  a stop-over to sites such as retail, banks, gas
  station, restaurant, etc.
• Trip generation rate number of vehicular
  movements to/from a site during 24-hour period

9
Trip Purpose

• Production vs. Attraction trip ends
• Home based trip
• At least one end in home (origin or destination)
• Work, school, shop
• Non-home based trip
• Neither end of trip at home
• Can be difficult to estimate

10
Roadway Level of Service (LOS)

• Roadway capacity is defined as the ability to
  accommodate traffic
• Service flow volume is the level of traffic flow
  (vehicles per day) that can be accommodated at
  various levels of service

• Roadway Capacity Ratings
• LOS A - Free traffic flow
• 0 - 35 of capacity
• LOS B - Stable traffic flow
• 35 - 50 of capacity
• LOS C - Stable traffic flow
• 50 -62 of capacity
• LOS D - High-density stable traffic flow
• 62 - 75 of capacity
• LOS E - Capacity level traffic flow
• 75 - 100 of capacity
• LOS F - Forced or breakdown traffic flow
• 100 of capacity

11
(No Transcript)
12
Site Impact Analysis Steps

• Identify location and determine site variables or
  setting
• Estimate trips generated by site
• Determine extent of area and streets impacted
• Assign estimated trips to local street network
• Conduct highway capacity analysis
• Determine traffic mitigation measures

13
Site location and setting

• Existing site use
• Proposed use
• General plan and zoning designations
• Local street and highway network
• Existing levels of traffic and turning movements
• Capacity of street network
• Planned improvements

14
Trip Generation Estimate

• Determine the number of vehicles that enter or
  exit the site of interest during specified time
  periods
• Primary information source
• Institute of Traffic Engineers (ITE), Trip
  Generation, 7th ed.
• Institute of Traffic Engineers (ITE), Trip
  Generation Handbook, 2nd ed.

15
Calculating Trip Generation

• Example Trip Generation Rates
• San Diego Trip Generation Manual
• (download from class web site)

16
Trip Generation Worksheet
17
Existing Traffic
18
(No Transcript)
19
Future Traffic w/Project
20
Evaluate roadway capacity
21
Thresholds of Significance

• ITE recommendation Any proposed site plan or
  subdivision plan which would be expected to
  generate over 100 directional trips during the
  peak hour of the traffic generator or the peak
  hour on the adjacent streets, or over 750 trips
  in an average day.

22
Typical Development Thresholds
23
Content of Traffic Impact Analysis

• I. BACKGROUND 
• Description of proposed development 
• Identification of peak hours and whether weekends
  will be used in the impact analysis
• Description of study area
• Location of proposed access points
•  II. BASE TRAFFIC CONDITIONS 
• Description of road network and intersections
  adjacent to site and at access points
• Counts during peak-impact hours 
• III. SITE TRAFFIC GENERATION
• Trip generation rates used and the source of
  these rates
• Traffic generated during peak impact hours
•  IV. SITE TRAFFIC DISTRIBUTION
• Method used to distribute traffic
• Table showing estimated traffic movements by
  direction
• Discussion of method used for traffic assignment
  and assumptions for assignment of traffic to
  network

• V. NON-SITE TRAFFIC PROJECTIONS
• Definition of design yearopening of proposed
  development
• Identification of development in study area whose
  traffic is to be included in calculations
• Adjustments of off-site through traffic volumes
• Assembling of off-site traffic forecast for
  design year
• VI. TRAFFIC ASSIGNMENTS
• Assignment of peak-period traffic to
  intersections and access points
• Figures for existing peak impact traffic hours,
  site traffic and total traffic
• Recommended access design improvements
• VII. REVIEW OF SITE PLAN
• Internal Reservoir at access points
• Parking layout
• Loading dock locations and access, including
  design truck used
• Recommended changes 
• VIII. DISCUSSION OF FUTURE TRAFFIC CONDITIONS
• Other developments in area