Fire departments across Texas are having to wait longer than usual to update their ambulance fleets, which is driving up costs and forcing many of them to use outdated vehicles to keep up with calls.

Why it matters: First responders need reliable, maintained ambulances without high mileage to ensure fast response times.

• But the ongoing microchip shortage, global supply chain issues and slower plant output have made it harder to replace older ambulances.

Driving the news: Fire officials across Texas are drafting a letter to U.S. Transportation Secretary Pete Buttigieg to urge his department to help them find a solution, Arlington Fire Chief Don Crowson tells Axios.

• Dallas Mayor Eric Johnson recently wrote his own letter to Buttigieg, asking for help. He said the delays jeopardize public safety in Texas and across the United States.

Threat level: Garland used to get new ambulances within four months of ordering them. The wait time is up to a year because of supply chain issues, a fire department spokesperson tells Axios.

• In Dallas, the wait time between placing the order and delivery is now at least 24 months, per the mayor's letter.

Of note: Severe weather around North Texas in the past year has depleted the fleet even more. Dallas lost more than four dozen emergency vehicles because of flooding in August.

Zoom out: Austin usually orders around 15 new ambulances at a time to maintain its fleet of 80 to 90 vehicles. This year, the city has had to use older vehicles, increasing maintenance costs by $3 million, Johnson wrote.

• And Houston's order for Ford F-150s this year has been pushed to next year, which will cost the city more because the 2023 rates are higher.

Yes, but: Arlington isn't struggling because the city partners with a private ambulance company that invested in a new fleet during the peak of the pandemic.

• The Arlington fire chief still plans to sign the statewide letter to Buttigieg to help other departments make their case.

The bottom line: "The citizens depend on us to have a working dependable fleet, and it's a crucial issue. I hope the federal government will help us ensure these priorities are being met," Crowson says.