Headway versus Leeway
by Paul Niquette
Copyright 2007 by Paul Niquette. All rights reserved. 
Inspired by Streetcar Mystery in Puzzles with a Purpose

ating back centuries in nautical history, the word 'headway' was originally a contraction of the phrase 'ahead-way' representing forward motion of a vessel, as distinguished from 'lee-way', which referred to lateral drift.  In common usage, the word 'headway' has come to mean "progress toward a goal," and 'leeway' implies flexibility, freedom.  In transit systems, headway means the time between successive buses or streetcars or trains. 

Headway ranks alongside speed as a key indicator of service performance. Policy-makers in public transit systems have learned that ridership decreases sharply when headways are made longer than about 15 minutes.  The psychology is elementary.  Time spent standing around waiting to get on is far more annoying than time spent in motion waiting to get off (see the The Grumble Factor).  With headways less than, say, 12 minutes, planning is unnecessary; most patrons won't even bother to consult the time-table.

Nowadays, private automobiles compete successfully with public transportation in urban settings -- but by offering flexibility ('leeway', so to speak) more than speed.  Congestion and parking see to that.   With transit headways longer than 30 minutes, patrons abandon public transportation and take to the automobile -- hey in 'droves' -- this, despite much higher cost for commuting by car.  For example...

Back in 1960, a certain Inter-Mountain community operated a successful city bus service on 15-minute headways.  Ridership expanded steadily to the point that there would be standing-room-only for morning and evening commuters.  Traffic congestion and problems with downtown parking did not exist.

As a "common good," public transportation systems worldwide are subsidized.  In response to taxpayer complaints about the amount of the subsidy, the city raised bus fares.  Ridership steadily expanded, though, and so did suburbia.  During rush hours, all buses continued to operate with "crush loads."

Someone got the bright idea to reduce costs by upgrading the fleet with bigger buses and running them less frequently. It worked.  At 20-minute headways, the city operated with 25% fewer buses and drivers.  Oh, but then, despite explosive population growth, ridership began to decline.  People bought cars.

Reduced passenger loads allowed the city to increase headways still further -- to 30 minutes -- while selling off buses and laying off drivers.  Ridership plummeted. Soon there were two seats for every passenger.  By coincidence, cars began clogging the streets and downtown parking-lots filled up.

Finally, at one-hour headways, the buses ran virtually empty.  A certain essayist moved into the city in 1990 and took the bus to work every day.  Often as not, he would be the only passenger on board.  He was puzzled about that. One morning, his driver, an old-timer, reprised the headway history.

pproaching the end of the Petroleum Age, economics will doubtless become more significant in the choices people make for their personal transportation.  One might expect public transportation systems in the U.S. to become as popular as they were a hundred years ago -- indeed, as popular as they are today in many countries. 

Private automobiles will not be able to compete, despite all of their 'leeway', so to speak.  Congestion will become merely an unpleasant memory.  Nevertheless, policy-makers in public transit systems may have no choice but to make headways longer and longer for petroleum-powered buses.  They won't run empty, though.

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