The Department of Transportation has another iconic city location in its sights to ruin: Park Avenue’s precious half-mile from East 46th to East 57th Street. Although the scheme to widen medians between traffic lanes at this point is only in the “proposal” stage, with two designs under review, count on the DOT getting its miserable, ideologically driven way as usual. Why does Park Avenue’s commercial main drag — the most successful office corridor in the nation, home to great companies of many types — need grassy little plazas for Big Mac munchers and costumed cartoon characters like the ones that turned Times Square into a late-night comedians’ joke? A Park Avenue redesign would eliminate at least one vehicular traffic lane, thus diverting cars onto other avenues — and give congestion-pricing advocates cause to demand even tighter restrictions than the ones that have done little to break up Midtown gridlock.…