Depends. My commute home from my office has a 6km of a three-lane road and then a single traffic light. The road never gets backed up more than a couple km from the traffic light, so even dropping it to a single lane wouldn't make any real difference to the throughput. The speed you drive on the three-lane road also makes no real difference to the throughput as long as you get the same amount of cars through the traffic light at each cycle.

> as long as you get the same amount of cars through the traffic light at each cycle.

Isn’t this proportional to the number of lanes in the road?

The bit about speed prior to lights was meant to be separate from the bit about # of lanes. To clarify - I mean, e.g. that when there's 5km of free-flowing traffic before the lights, and then 1km of congestion, it doesn't matter how fast you drive for those 5km as long as it doesn't delay your passage through the lights. I could halve my speed from the speed limit for those 5km and still arrive at the congestion at the lights before it's my turn to go through them.

If all the lanes are used at capacity, yes. Otherwise, no.