off-ramp being the M10 (Solomon Mahlangu Drive; formerly Hans Strijdom Drive) east of the Waterkloof Air Force Base. It has Pretoria East to its east and Centurion to its west. Just after Solomon Mahlangu Drive, near the suburb of Pierre van Ryneveld Park, the R21 intersects with the N1 Highway (Danie Joubert Freeway; Pretoria Eastern Bypass), which is the freeway between Johannesburg and Polokwane. The Interchange is named the Flying Saucer Interchange. After the N1 Interchange, the R21 Freeway continues southwards and has 10 off-ramps and interchanges for the remaining 43 km length of its freeway section. The R21 intersects with the M31 (Irene Off-ramp), R562 (Olifantsfontein Off-ramp), R25 (Birchleigh/Tembisa Off-ramp), R23 (Benoni Off-ramp), M32 (Pomona Off-ramp), M43 (Atlas Off-ramp), M96 (Kempton Park Central Off-ramp), R24 (O.R. Tambo International Airport Interchange), M41 (Jet Park Off-ramp) and N12 (Rietfontein Interchange). After the M31 Irene off-ramp, the R21 leaves the City of Tshwane Metropolitan Municipality and enters the City of Ekurhuleni Metropolitan Municipality. From the M31 Irene off-ramp up to just after the O.R. Tambo International Airport, the R21 is followed by the M57 Metropolitan Route of Johannesburg from north to south (which can be used as an alternative route to avoid being charged fees by the e-toll system or when there are roadworks on the highway). From the R562 Olifantsfontein off-ramp to the R25 Birchleigh off-ramp, the R21 bypasses the township of Tembisa (forms its eastern boundary). At the O.R. Tambo International Airport, south-east of Kempton Park Central, the R21 meets the R24 Freeway, which connects the airport with Johannesburg Central in the west. Via the R24 (named the Albertina Sisulu Freeway), the R21 is the only freeway apart from the Ben Schoeman Freeway (designated as the N1) that links Pretoria with Johannesburg. North of Boksburg (just after the M41 Jet Park off-ramp), the R21 forms an interchange with the N12 Highway to Johannesburg in the west and Witbank (eMalahleni) in the east at the Rietfontein Interchange, which marks the end of the R21 being both a freeway and a toll road (e-toll highway). The R21 becomes Rietfontein Road when it junctions with the M44 Road (North Rand Road) at the next junction by East Rand Mall. Further south, at the suburb of Boksburg North, the R21 meets the M41 again and continues by way of a right turn at Rondebult Road. The R21 then meets the R29 (Cason Road) and