Agree with the above. And rather than running the trellises east to west, I'd align them north to south.

I put my Rattlesnake Beans on two trellises that are 2 feet apart and I get good harvests. I started using 3 trellises on a 2 foot bed but eventually reduced it to 2 trellises. See picture. The rows are running east to west.

Thanks for the picture and comments Yolos and other comments Kate and gardengal. I do appreciate the variety of ideas and certainly believe their are numerous approaches to gardening.

Assuming you're in the northern hemisphere, your northern trellis will be seriously shaded by the southern one. Plants will grow OK on each, but your fruit productivity on the shaded one will be drastically reduced. I tried this once with tomatoes. Never will again.

Ditto on Dan's comments. How closely you space your trellises depends upon how tall they are, what will be growing on them, and how much access will be needed for weeding/harvesting. You also want to consider air circulation, especially if you have had disease issues before, or live in an area where rainfall or high humidity is frequent.

As already mentioned, shading is the biggest issue. If you space trellised rows too closely, it will reduce sunlight - and yield - in the shaded rows. I use 6' trellises for many vegetables, usually running E-W. At my latitude, the shadow from those trellises stretches 42" for most of the growing season, so that is the spacing I use; the vines bear at all points from ground to top. I might cut that down to 36" if the plants on the S side have relatively open foliage (such as yardlong beans).

In the past, I've used 30", and 36". Provided the vines all grow at the same rate, they are uniformly healthy until they reach the top. Once shade begins on the lower part of the plants though, those leaves will begin to die, and little will be produced there.

As a rule, I recommend running trellised rows E-W, to get the maximum amount of available sunlight. If you run multiple adjacent rows N-S, all rows will be shaded to some degree. I do sometimes run rows N-S, but then use shorter trellises (such as for cucumbers or tomatoes) or medium-tall crops (such as sweet corn) on either side.