Sounds like Passiflora caerulea.

Here is a link that might be useful: Caerulea flower and fruit

I don't know if Passiflora caerulea is hardy that far north. If it is a passie, it could be Passiflora incarnata also known as "Maypop". Many passies have variable number of lobes in the leaves - usually from 3 - 5, and that applies to incarnata.

If that's what you have, then when the egg-shaped fruit is ripe (turns purple and drops off the vine), it is edible as passion fruit!

Here is a link that might be useful: Passiflora incarnata (Maypop)

Sorry, not Passiflora. I have some more details from driving past it again this evening:-

• the leaves look very much like a maple's, they are not very deeply lobed

• it has many flowers; they are white and small, about the size of my little fingernail

• the seedpods have spikes or thorns all over them and are a mottled in a pattern similar to a watermelon's, but much smaller

Hope this is helpful in pinning it down!

Could it be a species of wild cucumber? The maple-like leaves and small white flowers sound right.

Are the fruits light in weight and "hollow". Does the plant climb by tendrils? These are a couple of other features that would suggest a wild cucumber genus/species...

Mike