These days in San Diego, people most often need ambulances on Thursdays.

Wayne Johnson knows this because he’s the guy responsible for making sure ambulances can show up at your door within 12 minutes of a major emergency. Johnson’s computer takes data from when anyone in the city used an ambulance over the last three years and predicts the busiest days of the week, times of day and locations for emergencies. Johnson deploys a fleet of ambulances across the city accordingly so they’re ready when the call comes.

Some of these computer predictions make sense: The city needs more ambulances in the afternoon and evenings than overnight because more people are out and about. Some of them don’t: Eight months ago, Saturday was the busiest day of the week, and Johnson has no idea why it changed.

“It’s kind of like a dance,” Johnson said.

Johnson works for Rural/Metro, the ambulance company the city entrusts to help deliver one of its most vital services. The company and the city’s Fire-Rescue Department both answer 911 calls for major medical emergencies. The Fire-Rescue Department aims to have a first responder on the scene of a medical emergency within seven minutes and 30 seconds, nine times out of 10, a target the department misses frequently. This is typically a fire engine.

Rural/Metro’s ambulances are supposed to get there within 12 minutes, nine times out of 10, a requirement that’s recently become more difficult for the company to hit.

The Fire-Rescue Department has a straightforward plan for responding to emergencies. It has engines and trucks scattered across 47 stations in the city, and fire crews typically return to their station after a call. Rural/Metro has a more dynamic plan. It relies on Johnson and his computer.

How the Ambulance Algorithm Works

Rural/Metro’s contract with the city requires the company to respond to high-priority medical emergencies within 12 minutes, and to lesser emergencies within longer timelines. Rural/Metro built its entire ambulance deployment system on meeting those requirements.

To help, the company bought a $300,000 computer program called MARVLIS – yes, it’s pronounced “marvelous” – for Johnson to use. MARVLIS calculates where ambulances need to go based on call histories and the location of the rest of the fleet. The program also shows Johnson what’s happening in real time.

An ambulance screamed down Broadway on a recent afternoon, and Rural/Metro spokesman Michael Simonsen peeked out the window of the company’s downtown office to look at it.

“Medic 68,” Simonsen said. “Where they going, Wayne?”

Johnson studied his screen.

“Hawthorne and State,” he said – an intersection in Little Italy. “Traffic accident.”

The program uses so-called heat maps to show potential trouble spots. Different trouble areas change depending on the time of day and what’s happening elsewhere in the system. Red represents the areas most likely to get a call, green represents the areas less likely to get a call and yellow is in the middle. Blue and purple represent the areas ambulances can respond to within the time requirements. Here’s one MARVLIS snapshot from Wednesday.

Ambulance Heat Map Sept. 18, 2013

Rural/Metro has determined it needs between two and three dozen ambulances on the street, depending on the time of day, to meet its 12-minute requirement. (To lesser emergencies, ambulances go without lights and sirens and they can take longer to get there.) Twenty four of Rural/Metro’s ambulances have an anchored home base that doesn’t change. They reside in fire stations in neighborhoods difficult to serve because of traffic or topography. These include Paradise Hills, Pacific Beach, San Ysidro and Rancho Bernardo.

The remaining ambulances, to use Johnson’s term, “float.” They’re posted at various fire stations or hospitals depending on where they’re needed, and the decisions are guided by strong patterns.

Johnson’s basically the architect of the ambulance deployment. Rural/Metro dispatchers in the Fire-Rescue Department’s communication’s center implement the system day by day.

This map shows a potential Rural/Metro ambulance deployment when all 36 ambulances are on duty. Remember: The system is dynamic and when ambulances are coming to and from calls, the rest of the system is positioned to fill in gaps.

Potential Rural/Metro Ambulance Deployment At Peak Hours

Rural/Metro delivers more patients to Scripps Mercy Hospital in Hillcrest than anywhere else in the city, Johnson said. An ambulance is almost always at the hospital, so the company usually never puts one at fire stations in the neighborhoods surrounding the hospital.

The San Ysidro Port of Entry is the busiest address in the whole city, Johnson said. The ambulance system gets calls from partiers-gone-sick and traffic accidents. Sometimes, Mexican ambulances drive Americans to the border and hand them off to Rural/Metro. The company has as many as three ambulances at one time serving the border and surrounding communities.

The Plan vs. Reality

Predicting the future doesn’t always work.

Some days, Rural/Metro doesn’t have a lot of emergency medical responses. This map from Sept. 10 shows the ambulances that were available throughout the day.  The lower the line, the more ambulances were responding to emergencies.

Sept. 10, 2013 Ambulance Response

Other days, the unexpected happens and the volume looks like it did on Sept. 3.

Sept. 3, 2013 Ambulance Responses

Lately, the picture has been more like the latter.

Over the past 18 months, the ambulance system has seen about a 25 percent spike in usage. Statistics would typically reveal what caused some of those increases, such as flu season or hot weather. But this time, Johnson said, complaints are all over the board, and he can’t tell what’s going on.

“Something happened,” he said.

Johnson speculated that the increase could have something to do with the economy and lack of health coverage. People then use the 911 system as their primary medical care. Ambulance companies around the county are seeing the same boost in numbers, he said.

Rural/Metro has put 1,000 more hours of ambulance coverage on the street a month than it did this time last year to deal with the increase. But it’s still having some trouble.

The company is exceeding its response time goals, but those figures exclude especially busy periods and other exemptions written into its contract. Without those exemptions, the company was responding within 12 minutes to highest-priority emergencies 87 percent of the time, not 90 percent, according to the most recent statistics.

City officials, who discussed response time issues as well as Rural/Metro’s recent bankruptcy at a Wednesday Council committee hearing, said they plan to do away with some of the exemptions in a future ambulance contract. Next month, interim mayor Todd Gloria is expected to have a timeline for when the contract might go out to bid.

The Bottom Line

When the contract does go out to bid, one of the most critical numbers will be the response time target – 12 minutes for highest-level emergencies is a county mandate. Companies, including Rural/Metro, will design their proposals to meet that timeline. The city’s fire union wants the Fire-Rescue Department to develop a plan, too.

Johnson said his company could develop a system that would get ambulances to major emergencies within five minutes instead of 12. But doing so would cost people who end up using the ambulances more money.

“We would build it that way and you’d be paying probably five grand per ambulance trip,” he said.

Liam Dillon was formerly a senior reporter and assistant editor for Voice of San Diego. He led VOSD’s investigations and wrote about how regular people...

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