Another handy Google Maps tool for transit

[tags]transit, google maps[/tags]

Google Maps has been a great tool for citizen planners to draw routes on street grids, such as the diagram used for the Pink Line threads and Chris Gerstle’s “Dodger Blue” subway.

Now, another tool can be used to take transit geekdom to new levels — in small steps, anyway. Behold, the distance measurement tool. It is a line that can be drawn between two points, or several points to plot out a trip. This can be a very practical tool for citizen transit planning. The tool could be used to calculate the average travel speed of a line. It can also be used to plot for a time point that is not listed on printed schedules.

With the distance calculator and that high school algebra most of us stuffed away in some distant corner of our minds, here is how both can be used.

Calculating average travel speed

This is something transit planners and schedules obsess over, while most riders only caring about their ride being “slow” or “fast”. The distance calculator can show just how fast that bus or train goes. Or, the calculator can provide a good “back-of-the-envelope” measurement for a run-time of a proposed bus or train route.

Now, here is the ingredients list for calculating the average speed of an existing service line:

• Google Maps Distance Measurement Tool
• Current timetable and route map
• Scrap paper or spreadsheet program for calculations
• Calculator or spreadsheet to perform calculations

Plot out the service following the exact route. Do not plot just the two endpoints. Curves and turns affect speed, so an “as-the-crow-flies” route would be inaccurate. Luckily, most L.A. bus lines follow the street grid, so there aren’t too many turns. Warning: beginners should not try to attempt plotting Metro Line 2 west of UCLA.

Once the route is drawn, take the calculation Google gives and use this formula:

Length of route / Time in hours

To find time in hours, take the run-time in minutes and divide by 60. A 75-minute run would be 1.25 hours, for instance. Here’s the calculation used for a Metro Line 16 trip from Cedars-Sinai to downtown Los Angeles starting at 7:30 a.m. on a weekday.

Click to enlarge with a short explanation.

The schedule shows a run-time of 44 minutes for that trip. Google Maps calculated the length of line at 8.56 miles. Plugging those figures into the formula, it would be 8.56/0.73. Doing the math, X yields an average speed of 11.67 miles per hour. An even more precise figure is found by the timepoint-to-timepoint times and getting their average. Line 16’s fastest segment is between La Brea and Western Avenues, traveling at an average speed of 17.14 mph. The slowest speed is the stretch between St. Paul Avenue and the end of the line at Main Street, at 7.46 mph. Between Vermont and St. Paul avenues, Line 16’s average speed with within the 10 mph range. The added precision yields an average of 11.47 mph. So, a Line 16 trip has a speed of 11-12 mph.

The Line 316 trip leaving after that Line 16 trip posts a better end-to-end average speed of 13.88 mph. The more precise timepoint-to-timepoint yields a higher speed, 14.24 mph. (This is because Line 316 has parts of the line where it serves local stops). Using the more precise speed, Line 316 yields a time savings of almost 25 percent. The 25 percent is also the target Metro tries to meet with Rapid service.

Guesstimating average travel speed

What to do if no schedule exists, such as for a proposed line? The rules change a bit. The formula stays the same. Several operational constraints must be accounted for, and transit planners have the most precise tools to account for these. When this is not available, the best amateurs could do is come up with a range of times. This time, though, the length must be divided by the average speed, and then that figure must be multiplied by 60.

Here’s an estimate of running speeds for the Expo Line. In this case, though, some information is already available. The Expo Line shares tracks with the Blue Line, and we have an idea of how long times would be along Flower Street. For now, these times could be extrapolated to similar distances. The average speed from 7th Street Metro Center to Pico Station is about 22 mph.

Click to enlarge with a short explanation.

For plotting out ranges, the following ingredients are needed:

• Google Maps Distance Measurement Tool
• Spreadsheet to perform calculations

Plot out the line as close to the actual route or alignment as possible. Copy the distance the calculator produces. Now, since the time is unavailable, solve for the time by using a range of estimate average speeds. For buses, these could be a target of 10 mph to 20 mph for locals, and higher for express services. For rail lines, these could be from 15 mph to 30 mph. For Expo, a sample range of 20 mph, 25 mph and 30 mph was used.

For added precision, the stops were plotted. Here is Google Maps’ distances for Expo Line stations:

Points	Distance (mi.)
7th-Pico	0.75
Pico-23rd	0.75
23rd-Jefferson	0.69
Jefferson-Vermont	0.86
Vermont-Western	1
Western-Crenshaw	1.54
Crenshaw-La Brea	1.16
La Brea-La Cienega	0.98
La Cienega-National	0.84

Altogether, the first segment of Expo comes to a little over 8.5 miles. Now, a range of average speeds should be used for estimated schedules. If these were the overall averages, an end-to-end trip would take about 26 minutes, 21 minutes and 18 minutes from Culver City to downtown L.A. at 20 mph, 25 mph and 30 mph, respectively. Times were rounded up to the next minute. Notice less of a speed advantage between 25 mph and 30 mph than 20 mph to 25 mph.

Comparably, a Line 333 takes about 35 minutes to cover a similar distance, and a Line 368 about 45 minutes.

Guesstimating an unlisted stop

There are so many bus stops on a line that not every single one can be listed. With a little work, Google Maps can come up with the unlisted times. For this example, an infrequent bus line is used, since it has a better chance of adhering to a schedule. Reliability decreases as the frequency increases.

Today’s volunteer is Metro Line 169. How would you discover a stop, such as Saticoy Street and De Soto Avenue, that is not listed? By again finding out the average speed. The overall end-to-end speed could work, but an even more precise calculation would be to take the average speed of the two timepoints the unlisted stop is between. In this case, it would be West Hills Hospital and Winnetka Avenue. The schedule shows 14-17 minutes. A 15 minute trip is used.

Click to enlarge with a short explanation.

Google Maps shows the distance between the timepoints at 4.15 miles. At 15 minutes, the bus travels at a rate of 16.6 mph. Now, to find De Soto, re-plot West Hills Hospital to De Soto Avenue. The calculation must be done from the direction the vehicle is approaching the stop.

The new distance is 3.16 miles. If the bus is traveling at an average speed of 16.6 mph, that 169 bus should arrive at De Soto approximately 11 to 12 minutes after the time listed for West Hills Hospital.

This category shall be rendered obsolete once agencies code up their schedules to interface with Google Transit.

Conclusion

Google Maps is a very useful tool for both professionals and citizen planners. The maps can take lines, boxes and pinpoints, which can show just how a line would run, along with boxes for images, videos and text. The distance calculator goes one better, as it can give some idea of just how fast a service can run.