Green Goblin drops a fully loaded Cable Car off of a bridge, Peter catches it with a single strand of Webbing and a single arm.

We can see that the Cable Car in the scene is the Roosevelt Island Tram, which has a weight of 41,525lbs when fully loaded according to the Official Website:

This is equivalent to 18,835kg, so approximately 19 tons. However the Webbing didn't just support this weight, it was able to catch it in free fall. To calculate the Impact Force we can use this Online Calculator. We need three values:

• Mass
• Height at which the Car was dropped from
• Distance traveled after initial impact

We already have the Mass of 18,835kg via the specifications. Counting from the gif, the Cable Car is in free fall for 27 seconds, and just roughly eyeballing the distance it fell, I think 15 meters is a fair estimate for the distance it fell, just for reference, this structure is 15 meters in height:

Now all we need is the distance traveled after impact:

It doesn't travel too far, I think 2 meters is a safe bet for the distance. Now we can just plug the three values into the Online Calculator previously linked, we get:

1,384,373 Newtons which is equal to 311,219 lbs of force, or 141 Tons of Force.