Lec 21, Ch.16, pp : Highway design standards (Objectives) Understand how highways are functionally classified Learn what factors are considered in a typical highway design Learn design standards for major parts of highways Learn the elements of highways (mostly from reading)

What we cover in class today… Functional systems of urban roads and rural roads Factors influencing highway design Design standards: (once after target functional class is determined) Design hourly volume, Design speeds, Elements of cross section

Highway functional classification Mobility Access Principal arterials Minor arterials Major collectors Minor collectors Local roads and streets

Functional system of urban roads Small urban areas: Population 5,000 to 50,000 Large urban areas: Population 50,000 or more Urban principal arterials Serves the major activity centers: Interstate, expressways, other principal arterials I-15, State St., University Ave., University Parkway, 900E, Center St. Urban minor arterials Interconnect with and augment principal arterials Bulldog Ave (1230N), Freedom Blv., Geneva Rd. Urban collector streets Collect traffic from local streets and convey it to the arterial system Canyon Rd., Timpview, 500N, 800N Urban local streets All other streetsThat’s where your house is.

Provo example – graphical presentation Principal arterial Minor arterial Collector

Functional system of rural roads Principal arterials Serves mostly interstate trips and a substantial amount of intrastate trips I-15, I-70, I-80, I-215, US89, US40, US6, US191, etc. Minor arterials Augments the principal arterials, connects cities, large towns, other large traffic generators SR73,10, 130, 257, 56, etc. Major collectors Carry traffic to and from county seats and large cities not served by the arterial system SR21, 24, 95, 18, 12, etc. Minor collectors Collects traffic from local roads and convey it to other facilities SR174, 124, 96, etc. Local roads All roads within the rural area not classified above All others

Rural roads example – graphical presentation Principal arterial Minor arterial Major collector Minor collector

Factors influencing highway design (Think of the Legacy Parkway in terms of these factors) Functional classification Expected traffic volume & traffic mix Design speed Topography Level of service targeted Available funds Safety Social and environmental factors

Guidelines for selection of design LOS (AASHTO: A Policy on Geometric Design of Highways and Streets, 2000) Functional Class Area & Terrain Type Rural level Rural rolling Rural Mtns Urban & Suberban FreewayBBCC ArterialBBCC CollectorCCDD LocalDDDD

Design hourly volume If we design a highway for the highest peak hour volume in the year, the highway will be too expensive. Researchers found that the 30 th highest hourly volume would be a comfortable compromise. This is the so-called “K” value. DHV = AADT*K*D where D is the directional factor Rural K= , Urban K=

Design vehicle The design vehicle is that vehicle selected to represent all vehicles on the highway.  Weight, dimensions, and operating characteristics. Its turning characteristics are very important for intersection and turning roadway design. See Chapter 3.

Cross section elements

Cross slopes High-type pavements: 1.5% to 2.0% Intermediate-type pavements: 1.5% to 3% For quicker drainage.

Barriers A typical roadside barrier (with guardrail…) Without guardrail… (Top two pictures taken from the WPI website) Conc. Median barrier Barrier and mountable curbs Click this picture for a simulation

Roadside design

“Forgiving” highway concept By improved design of the geometry of highway or by the use of various equipment, highways were made safer. These equipment reduce the severity of impact or allow the driver to steer back to the traveling lane. (Pictures extracted from WPI’s web page, Worcester Polytech Institute, MA) * Shock Absorbers at the gore area

Breakaway sign posts POZLOC.com