Extreme Heat Warning: Dangerous Heat Wave Targets Millions of Holiday Drivers Across the East Coast

A heat wave has the Northeast in its grip for the Independence Day weekend. The Extreme Heat Warning covers Interstate 95 from Washington to Boston, the spine of the region, and it holds through Saturday. If you are driving for the Fourth of July, the hottest conditions land right on the busiest travel days. Tens of millions of people live along this stretch, and many more will drive it over the holiday.

New York City is the hottest link in the chain. The National Weather Service there warns of a heat index of 105 to 115 into Saturday evening and says the heat could bring "impacts to transportation infrastructure and electrical and water systems." The warning runs from Washington and Baltimore up through Philadelphia and into Boston, with the highest readings near the big metros and overnight lows only in the 70s and low 80s, so roads and vehicles never fully cool down.

Peak Driving Danger Window

Daily from about 1 PM to 8 PM Friday and Saturday, when the heat index tops 105 to 115 along I-95. Warnings run through 8 to 9 PM Saturday across Washington, Philadelphia, New York and Boston.

Where The Risk Is Highest

The through routes carry the load. I-95 threads all five metros in one line, with I-76 in Philadelphia, I-495 and I-66 around Washington, the Garden State Parkway and I-87 in the New York area, and the I-90 Mass Pike and I-93 into Boston.

What Extreme Heat Does To Your Car

Extreme heat is a health warning, but it is also a driving hazard, and the effects show up fast. A parked car is the clearest danger. The National Weather Service repeats in every bulletin that an interior reaches lethal temperatures within minutes, which is why children and pets should never be left inside, even briefly.

On the road, heat this strong can buckle pavement and cause concrete to blow up into sudden ridges, the kind that damage tires and send drivers swerving. Overheated, underinflated tires are more likely to blow out at highway speed. Engines run hot in stop-and-go holiday traffic, and coolant systems get pushed to their limits. Electric vehicles lose range in the heat and charge more slowly, so the buffer you planned on may be smaller than expected. None of this is in the weather bulletin, but all of it is what heat like this does to traffic.

Related: EVs Lose Far Less Range Than Most Drivers Expect

What Drivers Should Do

• Never leave anyone, child or pet, in a parked car, not even for a minute.
• Check tire pressure before a long drive, since heat raises pressure and worn tires fail faster.
• Carry extra water in case you are stuck in holiday traffic or break down on a hot shoulder.
• Watch the temperature gauge in slow traffic and run the air conditioning to help cool the engine bay.
• If you drive an electric vehicle, plan for reduced range and slower charging, and leave a wider margin.

Away from the coast, the same heat wave stretches west across the Ohio Valley, the Mid-South and the Plains, with more triple-digit heat index values on other major corridors. Separately, drivers heading to the Southwest should note that wildfires have closed roads there, including State Route 89A near Sedona, Arizona.

This is a developing heat wave. We will update this story as the National Weather Service extends or changes the warnings and as holiday road conditions evolve. Check your state 511 service and the local National Weather Service office before heading out.

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