I’ve heard Haussmann set many boulevards at about 30 m so daylight could reach 5–6 story facades and to move troops — does anyone have primary sources showing which rationale drove the section? As someone who lays out streets and plazas, I’m curious how that width balanced light, tree pits, and carriage turning in the 1850s.
If you want a primary, Haussmann’s Mémoires (vol. 3) frame the 30 m sections around ‘salubrité et circulation’, and the 1859 Règlement de voirie standardizes about 30 m with double tree rows — more hygiene/flow than barricade-busting. For laying out, think about 2×5 m sidewalks + about 20 m carriageway, which fits two alignments of pits and turning radii while keeping decent daylight for 5–6 stories at Paris latitude.
One angle to check: Belgrand’s sewer works tied the big “collecteurs principaux” to double tree rows, and his plates break a about 30 m boulevard into carriageway, tree belts, and sidewalks — so it wasn’t just for parading regiments. Pull a plate from Les Travaux souterrains de Paris and you can scale the pits and curb-to-curb to test turning. @OP curious which boulevard you’re modeling.