HIGHWAY DESIGN PROCESS& ROUTE LOCATION

Spring 2015

● Sponsoring Agency

● Highway Classification

● Design Speed

● Cross sections

● Maximum Superelevation

1. Identify Sources and Jurisdiction of Design

Standards

● Topography (flat, rolling, mountainous)

● Ground conditions

● Possible adverse environmental impacts

● Habitation and property

● Acquire right-of-way

2. Major Characteristics of Site and Vicinity

● Design speed

● Minimum horizontal curve radius

● Maximum allowable grade

● Cross section elements

● Maximum allowable excavation depths and embankment heights

3. Establish major Design Controls

Step 8

● Identify alternative routes

● Sketch horizontal and vertical alignments

● Screen alternatives and select routes for preliminary design

4. Select Route for Preliminary Design

Step 8

● Horizontal and vertical alignments

● Cross sections

● Mass diagrams

● Major drainage features

● Potential environmental impacts

5. Conduct Preliminary Design

Step 8

● Approximate project costs

● Approximate user costs

● Economic cost estimate

● Environmental impacts

6. Estimate Costs and Impacts

Step 8

● Economic cost comparison

● Environmental impacts

● Select preferred alternative for detailed design

7. Evaluate Alternatives

8. Modify Major Design Controls, if necessary

● Prepare detailed design

● Prepare tender documents

9. Undertake Design of Selected Alternative

Route Selection

NATURAL AND MAN-MADE FEATURES

• Selection of possible routes, other than traffic considerations, is governed by:– Topographic features– Human habitation– Environmental features

• Therefore, you need to review the area’s major topographic features

TOPOGRAPHIC MAPS

• Maps available at the United States Geological Survey (USGS)– http://www.tnris.state.tx.us/datadownload/download.jsp

• Key Elements:– Identify suitable ground conditions: wetlands, rock

outcrops, flooding areas, and other features influencing construction activity (solid rock)

– Examine contour lines to estimate grades and steepness of terrain

TOPOGRAPHIC MAPS

• Key Elements (cont’d):– Define streams, rivers and ravines to indicate

possible need for bridges– Identify soil conditions (dependant on type of

maps)– Summarize findings on maps (see example)

• Need to look for: effects of ice and snow, avalanche area, cultural areas (native burial ground), school activities

Schoon (1999) Figure 1-1

Schoon (1999) Figure 1-2

Schoon (1999) Figure 1-3

Aerial Photography

• Key Elements:– Aerial photography can be used to confirm or modify

information on topographic maps– Can provide information about avalanches, mudslide

or flooding– Stereographic aerial photographs can provide general

ideas about grades– Oblique photographs can also provide general ideas

about grades– The presence of trees may make identification difficult

Schoon (1999) Figure 1-4

Schoon (1999) Figure 1-5

Other Maps

• Geological and Soil Maps– Can provide information for cut and fill

estimate (clay versus rock)– May provide information for pavement design

• Ground Surveys– Can be useful for very rugged terrain (since it

is suggested that the design engineer “walks the route”)

ROUTE IDENTIFICATION

• Balance between user costs and construction costs– Least user costs: higher design speed, shortest route,

etc.– Least construction costs: little if no cut and fill, few

bridges, no tunnels, etc.

• Maintenance costs (roadside devices, etc.)• Other societal costs

– Safety– Air and noise pollution

Schoon (1999) Figure 1-6

Schoon (1999) Figure 1-7

www.keeptexasmoving.com

www.keeptexasmoving.com

www.keeptexasmoving.com

www.nationali69.org

STATIONINGU.S. units

1+00.00

2+00.00

3+00.00

4+00.00

100 ft

1+000.000

1 km

2+000.000

3+000.000

4+000.000

Metric units

3+43.58 or 343.58 ft

2+458.218 or 2,458.218 m

Wright and Dixon (2004) Fig 13-3

Wright and Dixon (2004) Fig 13-4