The first thing you notice when you spend some time with the photo-radar-enforcement van is that every driver is speeding.

Well, maybe not every driver. Because the second thing you notice is that older (or more experienced, if you prefer) drivers save everyone trapped behind them a lot of money.

On this day last week, photo-enforcement agent Katie Salas has parked her specially modified van on Denver’s East 17th Avenue at Cook Street.

Now, you may think that locations such as this — a four-lane commuter route, near a high school, and across the street from a park — are chosen because they will produce the most revenue for the city. Not so, said Ted Porras, supervisor of Denver’s “photo enforcement unit.”

“We’re restricted to three areas: safety zones (like park boundaries), school zones and residential zones with posted speed limits of no more than 35 mph,” Porras explained. “Believe me, if we enforced along Colorado Boulevard, we would see more.”

Hard to imagine, because we are about to see plenty. But first, there are a lot of rules to follow in the photo-radar-enforcement- van business.

It must be parked in such a way that the radar can shoot across the traffic lanes, and so the operator will be able to clearly see every car the radar clocks as a violator.

Next, the big blue “PHOTO RADAR IN USE AHEAD” sign must be posted facing the drivers who are about to get cited. Denver requires it to be at least 325 feet from the van. Salas and Porras will mark off more than 500 feet for this “enforcement” activity because they want to make sure drivers are notified in plenty of time to see the 30-mph speed limit and know that the van is ahead. Their benevolence has nothing to do with the presence of a newspaper columnist. Of this I am certain.

Now, the system must be checked and calibrated. Salas must get her paperwork together to note the body type of every vehicle captured on camera as a violator. The system is then set to trigger at 40 mph, 10 above the posted speed limit, and, after more than 20 minutes of preparation, we are ready.

“Now, we wait,” Salas said. Not for long we don’t.

Beep. Flash. Beep. Flash. Beep. Flash. In the space of three minutes, five cars have broken the 40-mph barrier, and nearly every car that passed was going faster than 30. A total of 46 will earn $40 Penalty Assessment Notices before an hour is up. Everyone, including bus drivers, cops, firefighters and the sheriff’s deputy who flew past this day, gets their photo taken and a notice of violation in the mail. If fishing were this easy, it would be boring and it would probably be illegal anyway.

Lots of people think this should be.

Denver’s auditor said police should be forced to prove photo traffic enforcement has a safety benefit, or it should be closed as nothing more than a “cash grab.” (Denver collected more than $2 million in the last fiscal year from the combined red-light/radar programs). The legislature briefly considered a bill banning the cameras, but it has been set aside for now. Some argue that you don’t have to pay when the notice arrives in the mail — technically true, but if you ignore it they will just send someone out to serve you personally, and it will cost you at least $25 more unless you can get it dismissed. (Yup, you get to pay for the privilege of being personally served.)

So photo radar enforcement is with us for at least another year, and there are a couple of things you should probably know.

Flashing your headlights, swerving or hiding behind other traffic does not work. Neither does a middle-finger salute (Salas gets a lot of those). Your best bet is to hit the brakes. You might just slow down in time, and that’s OK with Salas.

“That’s what we’re here for,” she said.

There is indeed a person inside the van, and she is not Satan.

Salas is the mom of a school-age son, and, while she takes no particular pleasure in helping catch speeders, she harbors no guilt either.

“We enforce around elementary schools a lot, and I feel pretty good about that,” she said.

So, next time you see the big blue sign, please slow down. It will save you money, and if the van is there, there may be kids, parkgoers or construction workers nearby too. Maybe even give the photo-enforcement agent a nice wave.

Use all your fingers.

Chuck Murphy: 303-954-1829, cmurphy@denverpost.com, twitter.com/cmurphydenpost, facebook.com/cmurphydenpost