Section 3: Environmental Documentation
Anchor: #i1001528Overview
TxDOT performs assessment of the social, economic, and environmental impacts of a transportation project in varying stages of detail during the project planning and design process as required by the National Environmental Policy Act. (For more information, see the TxDOT Environmental Procedures in Project Development Manual.)
Traffic data are needed for environmental analyses and documentation to describe the project need and to assess the noise, air quality, and water quality impacts associated with each project. Each of these types of analysis requires a somewhat different type and level of detail in traffic data.
Anchor: #i1001545Traffic Data Provided
Description of Project Need. The need for a new facility or improvements to an existing facility is based on forecasted travel within the corridor or along the facility. Traffic data are used to show that the existing capacity is not sufficient to handle the forecasted traffic or that a new facility is needed to relieve congestion within the corridor. The traffic data required for most added capacity improvements include:
- base year AADT for the existing facility or for major facilities in the corridor for a new facility
- forecast year AADT for no-build alternative.
Analysis of Noise Impacts. Noise impact analysis requires the following traffic data for each link on the facility and major cross-streets of the alternatives under consideration, including the no-build:
- existing average weekday traffic with peak hour and directional factors, or existing directional peak-hour traffic
- design year average weekday traffic with peak hour and directional factors, or design year directional peak-hour traffic
- existing and design year average travel speeds
- vehicle mix volumes or percentages for the peak hour for autos, medium duty trucks (two-axle, six-tire), and heavy-duty trucks (three-axle and above).
Air Quality Impacts. Air quality analysis for project level environmental work requires the following data for each link for all alternatives, existing and no-build:
- average weekday traffic with peak hour and directional percentages or directional peak-hour volumes for the estimated time of project completion (ETC), ETC + 10 years, and ETC + 20 years
- average speeds for ETC, ETC + 10 years, and ETC + 20 years
- vehicle mix volumes or percentages for ETC, ETC + 10 years,
and ETC + 20 years for eight classes of vehicles:
- light duty gas vehicles
- light duty gas truck 1
- light duty gas truck 2
- heavy duty gas vehicle
- heavy duty diesel vehicle
- light duty diesel vehicle
- light duty diesel truck
- motorcycle.