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Comparison of Link light rail versus Bus Rapid Transit trunk (main) line capacity

R.C. Harkness, PhD

March 11, 2003

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Executive Summary

Some people still think buses have insufficient trunk line capacity to meet the region's long-term needs along the north south "spine". At the same time they believe light rail does have adequate capacity. They see capacity as the overriding strategic reason for building light rail. Do the facts support these beliefs?

This whitepaper compares the ultimate people moving capacity of light rail (LRT) and bus rapid transit (BRT) in the I-5 and I-90 corridors. The objective of the paper is to determine whether trunk line capacity is a valid criterion for choosing one technology over the other, and if so which technology is superior.

Data about Link light rail's capacity, and forecast demand, comes from Sound Transit documents. This is compared with estimates of BRT capacity as well as actual observed volumes on several heavily used BRT systems. Key results are summarized in three charts.

Key conclusions from this paper are:

  • The trunk line capacity of Sound Transit's proposed Link light rail is severely constrained by local conditions particular to Seattle. Link light rail has nowhere near the people moving ability of heavy rail systems like BART or the Washington DC METRO.
  • Capacity on Links south line is limited to one third of what the north line could carry. This forever shortchanges the entire south end in terms of regional transit capacity.
  • The likelihood of building light rail in the I-90 corridor is remote since it would reduce the people moving capacity in that corridor to well below what a mix of BRT and other HOV vehicles could achieve.
  • Buses operating on HOV lanes are capable of carrying several times more passengers than Link light rail will ever be able to carry. (over 50,000 persons per hour each direction for BRT, versus 16,400 for Link light rail)
  • Sound Transit's estimated year 2020 passenger demand for Link light rail is far below the systems capacity, and could easily be handled by a modest BRT system.
  • Understanding the ultimate useable capacity of either light rail or BRT requires additional analysis of how people will access the rail stations or how buses will access the HOV lanes under full load assumptions.
  • Both light rail and BRT have far more capacity than the region is forecast to require in 2020. Therefore finding ways to increase demand, not worries about having adequate supply, should be everyone's main concern.
  • A misplaced focus on capacity has been diverting attention from the real issue. The real issue is: for an investment of X Billion dollars, which technology can attract the most riders?

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