Evidence from the recent freeway holdups in the US indicate that it's not much of a problem. A stationary car with just lights and heat on low would use 1KW maybe 2.
So if we were to take your example using a typical EV like a VW ID3 which has a 58KWh battery.
On 60% charge it would have about 35KWh capacity. In winter conditions, assuming a consumption rate of 3.5m/KWh this means a range of just over 120 miles.
If you hit a 4-hour jam and insist on keeping toasty warm, you'd lose 8KWh or 28 miles of range, ie down to 92 miles.
