Suppose that there are three sections of roads in a city with a length of 3km, 5km and 10km respectively, and the street lamps are laid every 30m, one on each side. The total number of street lamps required for these three sections of roads is 202, 334 and 668, respectively. The traditional street lamps are based on the high pressure sodium lamp with a power of 250W, and the LED street lamps are based on the power of 50W for comparison.

The unit price of traditional street lamps is 1000 yuan/lamp, and the unit price of LED street lamps is 3000 yuan/lamp. The cost of light sources required for laying three lengths of traditional street lamps is 202 * 1000=22000 yuan, 334 * 1000=33400 yuan, 668 * 1000=668000 yuan, and the cost of light sources required for laying three lengths of LED street lamps is 202 * 3000=606000 yuan, 334 * 3000=1002000 yuan, 668 * 3000=2004000 yuan.

Let's analyze the cost of laying cables for two light sources on a three section road. The load flow of the trunk cable of the traditional street lamp on a 3-kilometer road is I=P/U=202 * 250/220=230A. It requires a copper core cable with a cross-sectional area of 60mm2, and its unit price is 120 yuan/m, so the cable cost is 120 * 3000=360000 yuan. The load flow of the trunk cable of the LED street lamp is l=P/U=202 * 50/220=44A. It requires a copper core cable with a cross-sectional area of 1mm2, and it requires a copper core cable with a cross-sectional area of 12mm2, The unit price is 12 yuan/m, the cable cost is 12 * 30=36000 yuan, the cable load flow of the traditional street lamp trunk line of the 5km road I=P/U=333 * 250/220=377A, which requires a copper core cable with a cross section of 90mm2, the unit price is 180 yuan/m, the cable cost is 980 * 5000=900000 yuan, the cable load flow of the LED street lamp trunk line I=P/U=333 * 50/220=73A, which requires a copper core cable with a cross section of 20mm2, the unit price is 25 yuan/piece, and the cost is 25 * 5000=125000 yuan, The cable flow of traditional street lamp trunk line of 10km road I=P/U=666 * 250/220=680A, which requires a copper core cable with a cross section of 400m2, the unit price is 360 yuan/m, the cable cost is 360 * 10000=3600000 yuan, and the cable load flow of LED street lamp trunk line I=P/U=666 * 50220=146A, which requires a copper core cable with a cross section of 42mm2, the unit price is 60 yuan/m, and the cost is 600000 yuan.