This paper presents a simulated-environment study to determine the effects of noise level and source type on annoyance responses to different transportation noises. Noise sources used in the study were; road, railway and aircraft traffic whose noise levels varied between 30-55 dB(A) in L-eq (indoor). Pass-by number for railway and aircraft traffic had values of 8, 12 and 16 per 30 min, while road traffic was continuous during this period. 64 subjects attending three different sessions of 30 min each, filled in a special questionnaire during the experiments. At each session, the subjects performed two different activities (reading and listening) and thus in addition to the overall annoyance, the activity disturbance was investigated. The total of 192 answers were analyzed as individual values, group average scores and highly annoyed subjects (HA %). The overall annoyance in both group average scores (giving the best correlation with noise level) and individual scores, are presented in this first of the two companion papers. The noise and annoyance relationships determined for each source revealed very strong dependence on noise levels and the regression lines displayed a steeper increase in comparison with the previous results. The significance of the source-type effect on annoyance was found at the levels of 0.03 and 0.02 for the overall annoyance question (P < 0.05). However since this effect was significant only for half of the different questions asked, it can be said that the source type is not a highly deterministic factor while the respondents are concentrating on daily work at home. Railway noise appeared to be the most prominent noise source in the overall annoyance, especially at moderate and low noise levels. The results supported the view that L-eq = 45 dB(A) is an indoor noise limit indicating a crossover between the source-specific annoyance lines. The activity disturbance will be elaborated in Part 2. (C) 1999 Academic Press.