Both realistically, and just pure fantasy...
Realistically:
For main roads I'd look into installing SOX for retrofits ad casual replacements, SON and Cosmo for main roads - I'm not too keen on metal halide.
Main road SOX: Philips SRS201
Main road SON: Thorn Riviera, Phosco P678
Main road CPO: WRTL Airtrace, Urbis Evolo
Main road columns would consist mainly of two tone blue painted CU columns with long outreach brackets. 8 to 10m in heights would be used the most. Post-top would only be fitted if the bracket gets in the way of powerlines! (All lengths)
For side roads I'd install CFL (PL-T and PL-L) and SOX. If it's for a highly dangerous area I may be persuaded to use metal halide...
Side road SOX: Philips XGS201, Philips XGS103/4, WRTL Delta, WRTL 2601 & WRTL IRIS
Side road CFL (PL-T): WRTL Delta, Phosco P567
Side road CFL (PL-L): Thorn Celest, WRTL Iris
Columns would usually be of 5m, but 6m may be used on more intermediate roads. Side entry brackets would be used for all installations apart from maybe the Thorn Celest (and the 2601). Lanterns are to be fitted post-top in areas with high vandalism, or on corners with thin pavements. Columns will be painted two-tone green.
For areas that are prone to high vandalism, I'd use Vandalite Skyes and WRTL Vectra Gaza Strips.
Wow, quite a few lanterns, and that is my realistic one!
Motorways, I would use: SRS201s, Airtraces, Thorn Orus lanterns, Arcs, Iridiums, MRL6s and Pilotes.
Unrealistic one another time.