San Diego will try something new in its uphill battle to shrink emergency response times in the sprawling and increasingly congested city: roving “peak-hour” fire engines not connected to any station and deployed at busy times in busy areas.

City officials say they plan to add six peak-hour engines – three in July 2019 and another three in July 2020 – to help meet a goal of having emergency crews arrive at the scene within seven and a half minutes 90% of the time.

Fire Chief Brian Fennessy said this month that the city is meeting that goal about 79% to 80% of the time, predicting the peak-hour engines could significantly boost that.

The engines will operate with four-man crews from 9 a.m. to 9 p.m. each day in areas where response times have been weak, or where regular crews are not available because of training.

City officials say it’s crucial to have peak-hour engines during late afternoon and evening commute hours, when emergency calls are typically at their highest volume.

To fully staff all six engines, the city plans to hire 48 additional firefighters at a cost of $6.3 million per year. No capital costs are anticipated because the city has several reserve engines it can use.

Fennessy stressed that peak-hour engines are not a substitute for new fire stations in key geographic locations, which he called the ultimate solution to the city’s response time struggles.

“I’ve never considered serving any of the fire station gaps with peak-hour engines instead of, rather than in addition to, fire stations,” Fennessy told the City Council this month.

Peak-hour engines, however, can shrink response times in areas where new fire stations are badly needed, but where construction has been delayed by lack of money or other problems.

Fennessy said an example is a planned station on the edge of City Heights that outside consultants Citygate called San Diego’s No. 1 response time priority in reports published in 2011 and 2017.

City officials considered seven potential locations in the area before buying a Fairmount Avenue site in May that has significant environmental hurdles.

Those issues have prompted city officials to estimate construction of the three-story station won’t begin until fall 2020, frustrating nearby residents and community leaders.

Councilwoman Georgette Gomez, who represents many of the neighborhoods the station would serve, said it’s baffling that a consultant’s report called for a new station there in 2011 and the city is still three years away from construction.

Fennessy said land in the area is scarce and some other potential sites wouldn’t have had as great an impact on response times in the area.

He said, however, that a peak-hour engine would be ideal for the area until the new station opens.

Other parts of the city likely to be considered for peak-hour engines, based on the 2017 consultant’s report, include Pacific Beach, south University City, Torrey Pines, Rancho Bernardo, Sabre Springs and southeastern San Diego.

Three areas with weak response times slated to get new fire stations are north University City in 2020, Black Mountain Ranch in 2021 and the UC San Diego campus in 2022.

Additional new stations include one already under construction in Little Italy and one planned in the Otay Mesa area.

Peak-hour engines will save the city money compared with quickly filling all of the 12 emergency-response gaps identified by the consultant, Fennessy said.

The savings go beyond just the cost of building 12 new stations at roughly $15 million per station. Staffing a new station typically adds about $2 million per year to the city’s budget on an ongoing basis.