Arrested for driving unreasonably slowly

On a Saturday I was arrested by a traffic police who told me to pay a fine of TZS 30,000 for causing a traffic jam by driving unreasonably slowly on the highway. This offence is very strange to me and I doubt if it really exists though I decided to pay the fine in order to save the time I would have wasted by going to Court to contest the offence. Does this offence really exist in law or a police self-created the offence? What speed is regarded as “unreasonable speed that causes a traffic jam”?
BT, Moshi

It is an offence under section 56 of the Road Traffic Act [Cap 168 R.E 2002] to drive unreasonably slowly at a speed that is likely to cause traffic jam or annoyance to other road users. The law does not set the minimum speed which is regarded as an unreasonable speed. The reasonability of the minimum speed depends on the situation of the traffic. The test is whether it is safe for a driver to speed up but she/he drives so slowly and in such a way that his slow speed is likely to impede other road users or annoy them.