Catching up with Carla, a Gal with Gears

23 hours ago

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Older posts in this blog are a restatement of my 1979 linear regression travel time analysis. This work shows techniques that would make some good high school science projects in transportation economics and science. Newer posts explore physical and political-economic changes appropriate for the people of San Mateo County to burn less gasoline, and emit less CO2.

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Travel time equation for the bus, really disappointing results

I revisited my Google Apps Spreadsheet that calculates a linear equation for bus rider travel times given the distance traveled.

The problem is, I got disappointingly slow numbers when I used the San Mateo County 511.org website to get travel times for six plausible bus trips I might take.

I tried to push the linear regression calculations closer toward car numbers.

First I excluded two of the slowest in speed (miles per hour) trips. I had noticed that all buses between El Granada and San Mateo city make a 10 or 12 minute dogleg through south Half Moon Bay. I took out two trips that apparently force the rider to ride the dogleg.

Second, I added a bus trip that avoids the "dogleg" and is what I would consider very fast. This was a trip up the coast to a Pacifica grocery store right next to the last bus stop.

The result of leaning on the data to push the bus numbers toward plausibility was very disappointing. Here is what I see now:

Bus 11.55 minutes per mile with -10.64 minutes added to each trip.

Car 1.41 minutes per mile with 12.09 minutes added to each trip.

In algebra:

Given a trip of "miles, measured as the bird flies"

The travel time in minutes is:

For bus trip = 11.55 x miles -10.64 minutes

For car trip = 1.41 x miles +12.09 minutes

These are two linear equations expressed in words. These linear equations model the time performance of these two different systems of transportation.

The crossover point for these two equations is 2.24 miles. That means a 2.24 mile bus trip and a 2.24 mile auto trip would have the same travel time, using these equations.

The reason I call these results disappointing is I did similar bus and car calculations in the 1980's using data for trips made in suburban Los Angeles. I have unfortunately misplaced those records. But I recall the bus performance coefficients in Los Angeles were much closer to auto performance coefficients.

The difference in land layout affecting the bus coefficients is I presently live in coastal El Granada, California. Steep coastal range mountains separate my home from store and work destinations.

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I revisited my Google Apps Spreadsheet that calculates a linear equation for bus rider travel times given the distance traveled.

The problem is, I got disappointingly slow numbers when I used the San Mateo County 511.org website to get travel times for six plausible bus trips I might take.

I tried to push the linear regression calculations closer toward car numbers.

First I excluded two of the slowest in speed (miles per hour) trips. I had noticed that all buses between El Granada and San Mateo city make a 10 or 12 minute dogleg through south Half Moon Bay. I took out two trips that apparently force the rider to ride the dogleg.

Second, I added a bus trip that avoids the "dogleg" and is what I would consider very fast. This was a trip up the coast to a Pacifica grocery store right next to the last bus stop.

The result of leaning on the data to push the bus numbers toward plausibility was very disappointing. Here is what I see now:

Bus 11.55 minutes per mile with -10.64 minutes added to each trip.

Car 1.41 minutes per mile with 12.09 minutes added to each trip.

In algebra:

Given a trip of "miles, measured as the bird flies"

The travel time in minutes is:

For bus trip = 11.55 x miles -10.64 minutes

For car trip = 1.41 x miles +12.09 minutes

These are two linear equations expressed in words. These linear equations model the time performance of these two different systems of transportation.

The crossover point for these two equations is 2.24 miles. That means a 2.24 mile bus trip and a 2.24 mile auto trip would have the same travel time, using these equations.

The reason I call these results disappointing is I did similar bus and car calculations in the 1980's using data for trips made in suburban Los Angeles. I have unfortunately misplaced those records. But I recall the bus performance coefficients in Los Angeles were much closer to auto performance coefficients.

The difference in land layout affecting the bus coefficients is I presently live in coastal El Granada, California. Steep coastal range mountains separate my home from store and work destinations.

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