Traffic Impact Studies.ppt

1、Traffic Impact Studies,Introduction,What is a traffic impact study (TIS)?,A study to identify impacts to a roadway network due to a proposed development (or change to an existing development) Also commonly called traffic impact analysis (TIA).,Who Requires Them?,Governmental agencies (city, county,

2、state) require them to determine necessary mitigation for proposed development as a result of increased traffic demands on roadway network These agencies will have established thresholds regarding when studies need to be performed, such as: X number of generated peak hour trips Site impacts a high-a

3、ccident location Specific site access or safety issues are of concern,Why are they necessary?,Why are they necessary? Satisfy goals of growth management Transportation infrastructure is provided concurrently with the needs of development generated traffic Ensures that developers pay their fair share

4、 of transportation infrastructure improvements,Who performs TISs?,Usually consultants, hired by developers Professional Engineering (P.E.) licensing usually required,Procedure,Preliminary,Obtain plans/details from developer or architect Site visit Determine scope of project impacted intersection/roa

5、dways need for special analyses Accident Parking Site access,Area of Influence,Analysis Scenarios,Existing Future without project (baseline) Future with project,Analysis Scenario,Existing,Collect data on existing conditions,roadway/ intersection details traffic volumes determine level of service alt

6、ernative mode (e.g., bus, walking) usage determine current levels of any other special analyses (e.g., parking, accident),Analysis Scenario,Future w/o project (baseline),Traffic Growth,Determine growth rate of traffic between existing year and proposed year of project completion/occupancy historical

7、 traffic counts regression obtain from agency planning model Factor traffic volumes up to this year,Other Projects and Improvements,Factor in any traffic generation from planned, but currently un-built projects Factor in any planned infrastructure improvements,Planned and Programmed Improvements,Ana

8、lysis Scenario,Future with project (4-stage planning model),4-Stage Planning Model,Trip Generation Trip Distribution Mode Split Trip Assignment,Trip Generation,Trip Generation is the process used to estimate the amount of travel associated with specific land uses May be the most critical element in

9、the study How Determined? Find similar land use/facility and determine from studying that case ITE Trip Generation Report Hybrid and engineering judgmentespecially with mixed uses, such as shopping mall,Trip Generation,Use of report land use selection independent variable selection time period selec

10、tion choice of rate or equation be aware of data limitations,Trip Generation,Trip types Primary Pass-by Diverted,Primary Trip,Made for the specific purpose of visiting the generator New trips on the network,Primary Trip Type,Pass-by Trip,Trips that would have traveled on a street adjacent to a retai

11、l center even if the retail was not constructed Applied to retail land uses, for example Shopping centers Convenience markets Gas stations Fast food restaurants Results in reduction of New Trips (on adjacent street) attributable to retail center,Pass-by Trip Type,Pass-by Trip Type,Diverted Trip,Trip

12、s using a segment of the transportation system that they previously were not using to access the proposed development site Count as new trips where they travel on segments required to reach the site where they previously did not travel,Diverted Trip Type,Trip Distribution,Definition: determining gen

13、eral O-D percentages Can use zonal population and employment data Obtain guidance from agency regional planning model,Trip Distribution,Mode Split,Definition: percentage of trips using different transportation modes Must pay close attention to type of land use Downtown employees may be likely to use

14、 bus Cannot expect grocery shoppers to take bus,Mode Split,Trip Assignment,Definition: assigning trips to specific routes that link O-D pair,Trip Assignment,Impact Analysis,Level of Service (LOS) Determination,Signalized intersections Unsignalized intersections Includes access driveways Arterial seg

15、ments Freeway segments Performed according to HCM procedures,LOS Analysis Results,Driveway Safety,Entering sight distance Exiting sight distance Performed according to AASHTO Green Book procedures,Construction Impacts,Often ignored, but can be significant in some cases,MitigationRecommendations,Adja

16、cent Intersection Improvements,Re-time signal phases/cycle Convert unsignalized intersection to signalized intersection Consult signal warrants in MUTCD Re-channelize Add lanes/turn bays,Mitigation Fee Options,Proportionate share payments Local improvement district Interlocal agreement Latecomers ag

17、reement,Development of Regional Impact (DRI),A DRI is defined by Section 380.06(1), FS, as any development which, because of its character, magnitude or location, would have a substantial effect on the health, safety or welfare of citizens in more than one county. The state (FL) has established thre

18、sholds to determine when a development must undergo the DRI review process These determinations are made by the Florida Dept. of Community Affairs (DCA) using Chapter 28-24, FAC.,Site Considerations,Site Considerations,Careful consideration needs to be given to: Number of access points Location of access points Consult access management guidelines and dr