Wheels fall off rounding sharp turns. Engines overheat. Dead batteries strand officers until they can get a tow back to the police station. Tires blow out with alarming frequency on cars that have been driven too long and too far.

All in all, Houston police officers are stuck behind the wheel of a decaying vehicle fleet that in many cases has outlived its recommended lifespan.

Nearly one in four police vehicles - marked and unmarked - has exceeded the city's recommended mileage limit, which is 100,000 for marked cars and 120,000 for unmarked.

The number of marked vehicles driven longer than the recommended five years has more than tripled, from 289 in 2015 to 880 this year, according to a May fleet report and other records obtained by the Chronicle. Data released by Mayor Sylvester Turner's office last week showed a smaller share, 44 percent, of marked vehicles exceeding the five-year standard.

"I am very concerned about running these units as emergency response units in excess of the standard, particularly to the extent that we do," HPD Senior Officer Shawn Palin wrote to his superiors in an August 2015 email.

Palin warned of the need to buy new vehicles or systematically refurbish many of the fleet's current vehicles.

"We recognize there is an issue and Mayor Turner is working to address it," city spokeswoman Janice Evans said in an email.

The city just finished purchasing 215 new cars and is planning to buy another 250 cars, she said, which would amount to replacing 30 percent of the marked fleet during the mayor's first year in office.

Acting Police Chief Martha Montalvo said the department works to manage the resources it has as efficiently as possible.

Cars lack oomph

"Like any police agency around the country, HPD can always use newer vehicles for our fleet," Montalvo said in an emailed statement. "We, like other agencies, have to prioritize our budgets. For us, we have been fortunate that the Mayor and City Council have agreed to fund additional cadet classes to help grow our ranks over the next several years. The trade off, in some instances, results in an impact on funding allocated for equipment."

The situation nevertheless has raised concerns among rank-and-file officers.

"Just listen to police radio and you'll hear it - 'My car is overheating, I gotta pull off,' " said one manager who oversees an undercover unit, recalling a recent chase in which one of his officers was pursuing a car thief until his engine failed. "If you're trying to run after someone in a car with 120,000 miles on it, it's not going to do very good. The compression's just not there."

Acquisition of new police cars in recent years has dropped to the lowest levels since 1993, HPD records show, even as the department's command staff received 16 new Ford Explorers earlier this year.

The department acquired approximately 620 cars each year from 1993 to 1998 - the city's height of purchasing over the last 23 years.

Since 2011, however, the city has obtained on average 230 cruisers a year, a number officers say is far below what is needed to keep the fleet's vehicles safe and effective.

"We are in this position due to multiple years of under-funding," Palin told his superiors in the report. "I firmly believe (we need) to find a way to fix the problem, but any timely fix will require a significant financial commitment."

Numerous other departments across the country are facing similar challenges after cutting dollars for vehicle replacement several years ago in response to the economic downturn, said Tom Wilson, a former police officer at the Anne Arundel County Police Department in Maryland who is now director of the Washington-based Police Executive Research Forum's Center for Applied Research and Management.

"As times get better, it's very hard to play catch-up," he said. "(Departments) end up in this cycle where they're behind the 8-ball."

An aging fleet means more vehicles spend more time in the repair shop, forcing officers to double up in cruisers. That reduces police visibility and hurts productivity and efficiency, said Charles A. McClelland, who retired as police chief earlier this year.

'More demanding'

While civilians drive many cars at 100,000 miles or more, those miles aren't the same for police vehicles, he said.

"One hundred thousand miles in a police car would be equivalent to 300,000 on a civilian car," he said. "You don't drive over curbs and potholes at high speed and jam on your brakes at high speed, do you? It's more demanding driving on a patrol car, so it puts stress on everything - tires, suspension, fuel. … Patrol cars, because of shortages, they never cool off."

When they aren't being driven, police vehicles endure additional wear and tear because they're kept idling while officers write reports or conduct other work, he said.

In some cases, broken-down vehicles can keep officers from responding to emergencies.

Over the last 12 months, Houston's fleet management division created 2,214 work orders for towing department vehicles. One incident could include multiple work orders, Fleet Management Division Spokesman Jedediah Greenfield said.

Houston's vehicle standards are stricter than Harris County's - which recommends replacing sedans after 130,000 miles and trucks after 150,000 miles, said Dre Dupont, director of Harris County Fleet Services.

Other large cities around Texas replace their vehicles before they've been driven so far.

The Austin Police Department rotates marked vehicles out of service after 80,000 miles or eight years in service and unmarked cars after 100,000 miles or 10 years in service, according to a department spokesman. San Antonio phases out marked units after they are driven 70,000 miles; unmarked administration vehicles rotate out every 10 years and unmarked undercover vehicles are phased out every two years, a spokesman said.

The Fort Worth Police Department recently announced plans to replace about 270 vehicles, or about 20 percent of the department's fleet, at a cost of $8 million.

Safety first

Houston Police Officers' Union President Ray Hunt and Mark Clark, the union's executive director, both declined several requests to be interviewed for this story.

"Making sure that the cops are driving a safe vehicle is important," said Wilson, the PERF executive. "It's no different than ensuring your cops are coming to work with their bulletproof vest … and they have a firearm that's capable of defending their life or someone else's. At the same time, you've got a motor vehicle that they're depending on to get from A to B on routine stuff, to get them to help somebody in an emergency situation, and so you want to make sure you don't push these things to an extreme."