1 / 14

# Geometric Design (I) - PowerPoint PPT Presentation

Geometric Design (I). Learning Objectives. To understand the considerations and quantifiable aspects of geometric design. Locational Design. Consider Current land use Geology Future land use Existing infrastructure. Controls and Criteria (1). Design Vehicles (p. 168-173)

I am the owner, or an agent authorized to act on behalf of the owner, of the copyrighted work described.

## PowerPoint Slideshow about ' Geometric Design (I) ' - maddock-walters

An Image/Link below is provided (as is) to download presentation

Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.

- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -
Presentation Transcript

• To understand the considerations and quantifiable aspects of geometric design

• Consider

• Current land use

• Geology

• Future land use

• Existing infrastructure

• Design Vehicles (p. 168-173)

• Passenger cars, buses, trucks, RVs

• Physical characteristics: weight, dimensions

• Establish intersection radius, pavement markings

• Vehicle Performance

• Operating characteristics: accel/decel

• Impacts air quality, noise, land use

• Driver

• Information handling

• Reaction time

• Time to perceive + react to a hazard in vehicle’s path

• Expected/unexpected

• Speed

• Driver errors

• Traffic

• Composition and volume

• Average daily traffic (ADT) is not adequate

• Design hourly volume (DHV)

• 30th-highesthourly volume (30HV) in one year

• K-factor (% of ADT; 8~12% urban, 12~18% rural)

• Speed

• Operating Speed (typically the 85th percentile speed)

• Free-flow Speed (close to zero density)

• Running Speed (actual speed)

• Design Speed (as high as practical)

• Capacity

• Maximum hourly flow rate (per lane) under prevailing conditions

• Helps select roadway type

• Helps define needs

• Design level of service (LOS)

• Length of roadway that should be visible ahead of you in order to ensure that you will be able to stop if there is an object in your path

• Calculate the SSD for a vehicle traveling on your roadway at the design speed, and then make sure the actual sight distance that you provide is at least as great as the stopping sight distance

• Assume

• Driver eye height of 3.5 feet

• Height of object between 2.0 and 3.5 feet

• Reaction distance + braking distance

• Design standard: tr=2.5, a=11.2

• Decision sight distance

• Allow longer tr for information processing for different maneuver conditions (table 6-5)

• Passing sight distance

• Ensure safe passing maneuver (figure 6-5)

• 4 distance components (figure 6-6)

• At 70 mph

• SSD = 730 ft

• DSD = 1445 ft (maneuver E)

• PSD = 2480 ft

• Basic controlling expression

e = rate of superelevation

u = side friction factor (dep. on pavement, speed, …)

V = vehicle speed

R = radius of curve

• Overall design procedure

• Determine a reasonable maximum superelevation rate.

• Decide upon a maximum side-friction factor.

• Calculate the minimum radius.

• Iterate and test several different radii until you are satisfied with your design.

• Make sure that the stopping sight distance is provided. Adjust your design if necessary.

• Design the transition segments.

• Tilting the roadway to help offset centripetal forces developed as the vehicle goes around a curve

• General Practice

• Highways, no ice/snow

emax = 0.10

• Highways, snow/ice

emax = 0.06

• Traffic congestion or roadside development, limit speeds

emax = 0.04 ~ 0.06

e

1

• Design based on point where centrifugal force creates feeling of discomfort for driver