Alberta TransportationHIGHWAY GEOMETRIC DESIGN GUIDE – URBAN SUPPLEMENT DRAFT - NOVEMBER 2003

BASIC DESIGN PRINCIPLES U.A-8

U.A.3.2 Selection of DesignDesignation

As with the selection of the design descriptor,continuity of roadway configuration, e.g. dividedor undivided is desirable. Continuity of speed isalso desirable, but not often practical orachievable. Generally, design speeds used inurban areas are substantially less than those usedin rural areas. The Highway ServiceClassification must be maintained throughmunicipalities. However, the spacing ofaccesses, design speed, number of lanes,presence of parking lanes may not be the same asin the rural setting and some tradeoffs may bepractical and reasonable when local use of thehighway is taken into consideration.

The following table is a correlation between thecurrent rural designations and the proposedurban designations. When selecting an urbandesignation, as a minimum, the designer shouldstrive to provide the Suggested DesignDesignation.

Table U.A.3.2 Coordination of Rural andUrban Design Designations

Rural Designation Suggested DesignDesignation inUrban Setting

RFD – 130 UFD – 110RAD – 130 UAD–110 or UED–90

RAU – 214.4 -120(future 4 lane)

UED – 90

RAU – 213.0 -110RAU – 212.0 -110RAU – 211.0 - 110

UAD – 407.4-80 orUAU – 211-70

RAU – 210 -110RAU – 209 -110

UAD – 407.9-60 orUAU – 210 - 70

RCU – 209 -110RCU – 208 -110

UCU – 211.0-60

All Local Roads ULUNote: The pavement width has been omitted from the table insome cases because it was not relevant to the comparison.

U.A.4 DESIGN SPEED

Generally, when selecting the standards to beapplied to a given roadway, the basic parameterfor the selection of geometric standards is designspeed. In urban conditions for new constructionor major reconstruction this same approachapplies. When setting the design speed, serviceclassification and roadway function need to beconsidered.

It is desirable to provide a reasonable degree ofconsistency in the design speeds, operatingspeeds and subsequently the posted speedselected within each classification subgroup orgroup. For example, the posted speed for allminor Arterial roads within a municipalityshould be identical or near identical and typicallythe design speed is 10 km/h higher than theposted speed. Where the legal speed limit is notreadily available, designers may obtain thisinformation from the Department. Where thespeed limit is not posted in urban municipalities,the legal speed limit is 50 km/h. Driverexpectations are met in this manner. Whenselecting a design speed for a given roadwaywithin a municipality, the designer shouldreview the design speed of similar roadwaysbefore making a final decision.

Many urban roadways traverse existing built upareas where the physical, environmental andproperty constraints are frequently the prevailingcontrols rather than the design speed. Typicalgeometric design practice considers theconstraints imposed and then analyzes the designfor acceptability from the safety and operationalpoints of view. If the analysis concludes that thedesign is unacceptable, revisions are required tominimize the influence of constraints or tomodify the expectations of the driver. Thedifferences between the two approaches (that fornew urban construction projects and that forseverely controlled urban retrofit projects) areillustrated in the following flow chart: