of 12V electricity, rear coil springs and an updated dashboard for later models. The Trabant's designers expected production to extend until 1967 at the latest, and East German designers and engineers created a series of more-sophisticated prototypes intended to replace the P601; several are displayed at the Dresden Transport Museum. Each proposal for a new model was rejected by the East German government due to shortages of the raw materials required in larger quantities for the more-advanced designs. As a result, the Trabant remained largely unchanged for more than a quarter-century. Also unchanged was its production method, which was extremely labour-intensive. Production started from 34,000 p.a. in 1964, reached 100,000 p.a. in 1973, to a high of 150,000 in 1989. The Trabant 1.1 was a 601 with a better-performing 1.05-liter (), VW Polo engine. With a slightly modified look (including a floor-mounted gearshift), it was quieter and cleaner than its predecessor. The 1.1 had front disc brakes, and its wheel assembly was borrowed from Volkswagen. It was produced from 1989 to 1991, in parallel with the two-stroke P601. Except for the engine and transmission, many parts from older P50s, P60s and 601s were compatible with the 1.1. 1989–1991 In mid-1989, thousands of East Germans began loading their Trabants with as much as they could carry and drove to Hungary or Czechoslovakia en route to West Germany–the so-called "Trabi Trail". Many had to get special permission to drive their Trabants into West Germany. The cars did not meet West German emissions standards and polluted the air at four times the European average. A licensed version of the Volkswagen Polo engine replaced the Trabant's two-stroke engine, the result of a trade agreement between East and West Germany. The first prototypes were built in 1988, with pre-series cars appearing in 1989, but series production only began in May 1990 - By which time the two German states had already agreed to reunification. The locally built EA111-series engine was given the model code BM 820 by the East Germans; the plant also made 1.3-liter versions for the Wartburg 1.3 (BM 860) and the Barkas utility vehicle (BM 880). The model, the Trabant 1.1, also had minor improvements to its brake and signal lights, a renovated grille, and MacPherson struts instead of a leaf-spring-suspended chassis. By April 1991, after only eleven months, the Trabant 1.1 was discontinued. In total, 3.7 million Trabant vehicles had been