Cantilevered Boardwalks For Motorway Bridges?

Bridge over M9 Kilcullen Bypass on Sunnyhill Road. Image coiurtesy Google.

When Kildare County Council, or whoever was responsible, produced the spec for this bridge, (and the one over the M7 at the Bundle of Sticks Roundabout outside Naas), they left out foothpaths. Maybe it was lack of common sense and an attitude of "Sure, only cars go out there". Or perhaps it was due to penny pinching and lack of foresight and a narrow bridge was cheaper than one a couple of metres wider? Anyway, I'm wondering could boardwalks/cantilevered foothpaths be fixed onto the sides, exterior to the parapets?
It would obviously be impractical to install foothpaths on the inside of the parapets due to to both lanes being reduced in width. As it is, cars can't pass pedestrians safely without partially moving into the other lane. An article by Paul MacDonald, Kildare National Roads Office, on the construction of the M7 Newbridge Bypass and M9 Kilcullen Bypass is available on the Kilcullen Diary here.

The section about the earthing of the steelwork of the underbridge for the River Liffey is interesting—High voltage pylons can induce voltages and currents in conductors, potentially leading to different and hazardous potentials between isolated elements of a structure. Bonding them together eliminates these voltages and earthing a structure pulls the voltage down to ground (similar to the equipotential bonding in bathrooms, where metal objects such as drains, radiators, towel rails, water pipes and metal baths are bonded together):

Bridge over M9 Kilcullen Bypass on Sunnyhill Road. Image coiurtesy Google.