<prompt> Translate the following text to EnglishKwa sababu sehemu kubwa ya gharama za barabara ni fasta, gharama ya barabara ya kitengo kwa kipande mwanzoni hupungua haraka kama kiasi huongezeka na inaendelea kupungua kwa kiwango cha kupungua.  <response>: Because a large proportion of street costs are fixed,27 the unit per piece street cost initially declines rapidly as volume increases and continues to decline at a decreasing rate. 