Using GIS for Regional Transportation
SUTTON J, GIS Trans, USA
Southem California is one of the largest urbanized regions of the world and extends over 39171 square miles with a total population of over 15 million. The Southern California Association of Governments (SCAG) is the regional transportation planning agenc
Southem California is one of the largest urbanized regions of the world and extends over 39171 square miles with a total population of over 15 million. The Southern California Association of Governments (SCAG) is the regional transportation planning agency for 188 cities ranging in size from the City of Los Angeles (3.5 million population) to small communities with fewer than 50,000 people. These are grouped into 11 subregions, 6 counties (Imperial, Los Angeles, Orange, Riverside, San Bemardino and Ventura), and 5 Transportation Commissions, such as Orange County Transportation Authority. The region is illustrated in Figure 1.
The SCAG region faces some of the worlds most difficult transportation problems, including poor air quality linked to vehicle emissions, increasing traffic congestion on the freeways, low transit utilization and low density urban sprawl. Transportation performance is measured by Level Of Service (LOS) and vehicle miles traveled (VMT). The former provides a measure of highway congestion ranging from LOS A, no congestion, to LOS F which indicates severe congestion with the highway operating at >90% capacity. The 1993 Regional Comprehensive Plan (RCP) estimated that in 1990 more than 50% of the freeways were operating at LOS E & F during the peak hours and that the region was failing to meet federally mandated air quality goals. The VMT statistics measure the increasing distances that auto users are commuting to work - a large part of the increase in vehicle emissions is attributed not to increasing auto use but to longer distance commuting. The regional plan aims to reduce both VMT and LOS to more acceptable levels by the year 2010.
The strategy adopted to accomplishes this has several elements but two priority policies. To encourage travel choice an expansion of regional transit services, bus, regional rail and metro has been given top priority; followed by the development of High Occupancy Vehicle (HOV) or carpool lanes. The plan calls for the designation of 365 miles of HOV lanes on freeways by 2010 (there are 170 miles of carpool lanes at present with another 50 miles under construction). HOV or carpool lanes are reserved for autos with two or more occupants. The HOV policy aims to encourage ear pooling and thereby reduce VMT. Both policies, if successful, would increase average vehicle occupancy, reduce vehicle emissions and ease traffic congestion.
Other policies, such as developing low energy vehicles (LEV) and experimenting with road pricing, play a supporting role. The region expects to spend over $50 billion on transportation between 1990 and 2010, with the majority of expenditures going on transit operating subsidies ($23 billion) followed by transit infrastructure ($13 billion) and HOV lanes ($12 billion). New highway infrastructure and improvements to existing freeways are allocated $20 billion but the percentage increase in freeway capacity is relatively small. Southern California has accepted that there is no way to build a way out of the highway capacity problem (too expensive and too environmentally damaging) and instead has adopted alternate policies of traffic constraint and travel choice.
It should be noted that while the RCP recommends these policies, there is very little development control to ensure that these plans will be successful. SCAG has no enforcement powers as such and is primarily a planning and monitoring agency that advises the subregions, counties and cities. The only stick that SCAG is able to wield is that unless federal air quality mandates and other regulations are met, the region will not receive federal aid under the Intermodal Surface Transportation Efficiency Act, 1991 (ISTEA). This Act mandates Metropolitan Planning Organizations like SCAG to produce an annual Regional Transportation Improvement Program. Failure to produce this or meet targets threatens funding.
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