Roadway Design Controls and Design Criteria

[RD-Design Engineer]

For the purpose of a short educational webinar about the AASHTO standards on geometric design I have spent about three hours trying to define clearly what is the difference between design controls and design criteria - the AASHTO way - and I found it is clear in the AASHTO green book - AASHTO have listed all design controls on chapter 2 and later it explained the two main criteria: function of the road (local-collector-arterial-..) and context of the road (urban-rural)
but when I came to different DOT design manuals - I am a little bit confused about the specific meaning (through Montana DOT - Illinois DOT - Mass DOT - Caltrans)
Any help ?

 

[civilman72]

Example:

Speed Limit:
35 MPH (Local)
45 MPH (Collector)
55 MPH (Arterial)

Your design criteria is the Speed Limit, your design control is your road classification. The recommended values for the criteria are determined by the design control information.

 

[dik]

I don't know if this publication helps, but, it has a lot of useful information in it.

 

[RD-Design Engineer]

thanks all - but here some quick notes
civilman - your note is somehow related to what Montana DOT follows (for example) - but not other state DOTs
dik - that's nice document and combines a lot of useful information - though different from AASHTO approach - but thank you for the share

 

[dik]

AASHTO may have several documents that are applicable. The file that was attached had a lot of useful information in it.

Dik

 

[ACtrafficengr]

I hope I'm not confusing you more, but FHWA uses the term "controlling design criteria" for the most important design criteria.

The following 10 criteria are considered controlling for the design of projects on the NHS: Design Speed, Lane Width, Shoulder Width, Horizontal Curve Radius, Superelevation Rate, Stopping Sight Distance, Maximum Grade, Cross Slope, Vertical Clearance, and Design Loading Structural Capacity. Stopping sight distance (SSD) applies to horizontal alignments and vertical alignments except for sag vertical curves. Of the 10 controlling criteria, only design loading structural capacity and design speed apply to all NHS facility types. The remaining eight criteria are applicable only to "high-speed" NHS roadways, defined as Interstate highways, other freeways, and roadways with a design speed greater than or equal to 50 mph (80 km/h).

Revisions to the Controlling Criteria for Design and Documentation for Design Exceptions

 

[RD-Design Engineer]

Dear ACtrafficengr - you are actually confusing me more (LoL) - not you indeed: but FHWA, AASHTO and Dots
The use of lane width, and shoulder width as a design control is very confusing -

As per the AASHTO: those are design elements not design controls - I can understand very well that the design speed is a design control, the vehicle characteristics is a design control (minimum turning radii, turning envelopes, acceptable acceleration rates, decceleration rates, ...) , and so on
Traffic volumes and their characteristics are design control (amount of design year volume, accepted level of service, composition,PHF, ...) and the outcome of traffic volume and their characteristics are the ones who determine no of lanes and lane width - so how lane width and shoulder width be a design control ?