1. SPECIAL TRANSPORTATION STRUCTURES (Notes for Guidance ) Highway Design Procedures
Lecture
Six
Radu ANDREI, PhD, P.E.,
Professor of Civil Engineering
Technical University “Gh. Asachi” IASI

2. Highway design procedures
Determine the volume of current traffic
Determine the project traffic data for future the considered design life of the road
Select the type and the size of the road in order to accommodate the estimated traffic demand
Perform studies for route location survey,draw preliminary plans and profiles, undertake map study for all reasonable alternative routes, select the best route
Perform detailed study and design for the selected route
Problems
Additional Readings

3. Determine the volume of current traffic
Determine the current volume and type of traffic along the specific desired line ( e.g. where the traffic has to go) of your project , including the peak loads and directions.
You have to acquire sufficient traffic data in order to account for daily, weekly and seasonal variations.

4. Determine the volume of current traffic
The traffic investigations should be performed by using manual or automatic , fixed or portable counters , supplemented by Origine- Destination( O/D) studies implying Driver Interview ( minimum sampling 25%) or Driving Postcard ( 100% distribution desirable).
Also investigation of speed, travel time and route by using specific tests conducted in under varied traffic conditions should be undertaken.

5. Determine the project traffic data for future the considered design life of the road
Fifteen or twenty-year period is usually taken into consideration for the design life of a road.
Also you have to review and take into consideration the regional population trends, census data, transportation studies available from the other modes of transport such as railroads, bus companies and airlines and utility expansion studies available in the area from telephone, gas and water-supply companies.

6. Determine the project traffic data for future the considered design life of the road
Regional trends on motor-vehicle registration, motor-vehicle mileage and public transit use related with the industry and commerce trends should be investigated.
Also the master planning including new or transit highways, scheduled for activation prior to design year, should be consulted.

7. Select the type and the size of the road in order to accommodate the estimated traffic demand
At this stage a basic design decision on the degree of access control must be made and the desirable design speed shall be established, by using the average recommended values for judging the highway capacity, presented in the specific chapters devoted to highway capacity and design speed in this course.
These average data concerning the highway capacity may be modified and adjusted in accordance with pertinent local experience.

8. Perform studies for route location survey,draw preliminary plans and profiles, undertake map study for all reasonable alternative routes, select the best route
At this stage make the preliminary plans and profiles based on field studies for all reasonable alternate routes which satisfy the desire lines, analyze and compare them ( see the next slide )

9. Perform studies for route location survey,draw preliminary plans and profiles, undertake map study for all reasonable alternative routes, select the best route

10. Perform studies for route location survey,draw preliminary plans and profiles, undertake map study for all reasonable alternative routes, select the best route
select the optimal location by comparing cost estimates, road user benefits, capability of incorporating the alternates into the regional master plans, types of vehicles versus feasible design and operating speeds, traffic safety and other pertinent factors including the following:
- location of interchanges and intersections with respect to traffic and topography;

11. Perform studies for route location survey,draw preliminary plans and profiles, undertake map study for all reasonable alternative routes, select the best route
- frequency of steep grades and the need for slower lanes or reduced speed for heavy vehicles, thus reducing highway capacity and traffic safety;
- right-of-way problems and presence of historical sites , cemeteries , etc;
- suitability to stage construction and appropriate accommodation of traffic during construction period;
effect of local climate , degree of exposition of the road to drifting snow and ice;

12. Perform studies for route location survey,draw preliminary plans and profiles, undertake map study for all reasonable alternative routes, select the best route
- location with respect of harmonization with the other existing transport modes;
- the type and stability of the subgrade soil and its influence on structural design and costs;
- the impact of the new road on its environment;
- the financial feasibility of project

13. Perform detailed study and design for the selected route
Establish geometric criteria and design speed for each major segment of the project in conjunction with preliminary alignment and grade.
Preliminary intersection design must include in addition to geometrics, the layout of traffic signs and pavement markings.
The aesthetics of landscaping , of views from the highway and of road structures shall also be considered in this preliminary stage.

14. Additional Readings
Andrei R. Land Transportation Engineering, Technical Publishers, Chisinau, 2002
Garber j.N., Hoel A.,L, Traffic and Highway Engineering, revised second edition, PWS Publishing,1999