Math shows why county buses always look so empty

Las Cruces Sun-News
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The South Central Regional Transit District is reviving county bus service. In its fleet is a 28-passenger bus on display recently in front of the Doña Ana County Government building.

The South Central Regional Transit District (SCRTD) has been running buses to provide regional public transportation in Dona Ana and Sierra counties for a few years. The reports on ridership tend to highlight the total number of rides taken per year, but here is an ongoing curiosity around this question:

The SCRTD reports it carries many thousands of riders per year, but the buses I see are mostly empty. How can both of those can be true?

They are both true. Very few people actually ride the buses at a given time, but over a year the total number of rides does add up. Here is how it works, with a little math to tell the story.

For FY 2017, the latest numbers available, the SCRTD officially reported just under 12,000 rides total for the year. That seems like a lot, but how many riders would that take?

12,000 rides per year equals 1,000 rides per month, on average; 1,000 rides per month equals 250 rides per week, on average; 250 rides per week (Monday through Friday) equals 50 rides per day, on average.

What is a “ride?” When any person gets on a bus, rides any distance, and gets off, that is one ride. It can be anyone, any time, any location, any distance, any bus line.

So, if 50 people ride on any of the SCRTD buses per day, on average, for a year, that adds up to 12,000 rides. But, then, why do the buses look empty?

There are five bus lines in the SCRTD system, and each line carries a different percentage of the total ridership. Using those percentages we get the following average daily ridership per line:

BLUE has five riders per day on seven runs for 0.7 riders per run.

TURQUOISE has seven riders per day on nine runs for 0.8 riders per run.

ORANGE has nine riders per day on six runs for 1.5 riders per run (Orange Line schedule is not on the SCRTD Web Site

PURPLE has 11 riders per day on 10 runs for 1.1 riders per run.

RED has 17 riders per day on 13 runs for 1.3 riders per run

OTHER has one rider per day. (OTHER is a category in the SCRTD data list, but is not explained.)

This information says that the buses are carrying about one passenger, on average, on each run. If a bus carries more than one rider on any run, on another run it will carry less than one – which can only mean none.

And remember, there could not have been any more than an average of 50 riders per day, total, on all of the SCRTD buses, or the total number of rides would have been larger than 12,000 for the year.

So, the answer is yes. there can be a large total number of rides in a year, even though the buses look empty, and, in fact, often are empty. Both can be, and in this case, are true.

Also, consider that those riders won’t be the same people every day, but some of them will be, as they regularly go to work or school. Let’s say that half of the riders, or 25 of the 50, are regulars. Then say the other 25 rides may actually be taken by 200 different people at different times. On that basis, the whole bus line is serving 225 different residents out of the 110,000 in the rural county, or about 0.2%. In order to serve 1% of the residents, then, the buses would have to carry 60,000 riders per year.

The SCRTD says they are on the way to 30,000 riders per year. Using the same analysis as above, this would take 2,500 riders per month on average, or 125 riders per day. The line does not report having carried 2,500 passengers in any month in its history – this is a long way to go, and would still serve just 0.5% of our rural residents.

Bob Hearn and Mark Best are both residents of Las Cruces.


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