The best thing about pedestrian/cycling bridges and tunnels is that they cost soooo much less money to build since they have so much laxer requirements. The reason why we still have roman bridges standing is because the stress contribution of a human walking on it is basically zero. But start bringing in cars and trucks and see it crumble in a week
Pedestrian and bike infra for majority of cases in dense areas is objectively better in all metrics except human laziness and entitlement